Transnational Mobility, A1 Certification, And Italian Social Security (INPS) Assessments: The Evolution Of EU Case Law

1. Introduction

Under the applicable law perspective, international working acitivity has implications not only with respect to the national rules applicable to the employment relationship but also to the relevant social security legislation.

Regulation (EC) No. 883/2004 (so called, "Basic Regulation") – relating the coordination of the social security systems of EU Member States, EEA countries (Norway, Iceland, Liechtenstein) and Switzerland – provides for a key principle: in case a working activity is performed in different EU Member States, only a single social security legislation is applied.

Regulation (EC) No. 987/2009 (so called, "Implementing Regulation") defines the procedures for the correct application of the Basic Regulation.
The above-mentioned two Regulations must therefore be taken as reference for navigating the framework of EU social security legislation.
According to the general rule, the social security law applicable to the employment relationship—whether subordinate or self-employed—is the law of the State in which the work activity is carried out (lex loci laboris) (see Article 11 of Regulation 883/2004).
However, in certain specific situations – such as, among others, posting or work performed in two or more Member States (Articles 12 and 13 of Regulation 883/2004) – the applicable legislation is identified on the basis of different criteria, which may lead to the application of the law of the worker's State of residence or the State in which the employer carries out its activities or has its registered office or domicile.

In such cases, the single applicable social security legislation is certified in a specific document known as the A1 Certificate (Article 19(2) of Regulation 987/2009).

2. A1 Certificate and Issuing Procedure

La Certificazione A1 attesta la legislazione previdenziale applicabile al rapporto di lavoro (subordinato o autonomo), fino a quale data e a quali condizioni e, conseguentemente, il non assoggettamento alla legge previdenziale di altro Stato dell'UE (v. art. 19 Reg. 987/2009).

A1 Certificate certifies the social security legislation to be applied to the employment relationship (subordinate or self-employed), until which date, and under which conditions, consequently certifying the non-application of the social security law of any another EU Member State (see Article 19 of Regulation 987/2009).

The above-menioned certificate is issued following a procedure started:
– in case of posting, by the employer with the competent Institution of the State whose legislation is to be applied, or
– in case of work in multiple Member States, by the worker with the institution of his/her State of residence.

The competent institution issues an initial determination of the applicable legislation on the basis of the regulatory provisions governing the specific case (Articles 15 and 16 of Regulation 987/2009) and informs the institutions of the Member States involved.

The initial determination is provisional and becomes definitive after two months from the date on which it is communicated to the institutions of the concerned Member States.

If there is uncertainty regarding the identification of the applicable law, within the above-mentioned two-month period, the relevant institutions must determine the applicable legislation by mutual agreement.
If differences of opinions arise, the institutions must seek an agreement.

In the meantime, the person concerned is subject provisionally to the legislation of one of the Member States in disagreement, according to the following order (Article 6 of Regulation 987/2009):
1. the legislation of the Member State where the person actually pursues his employment or self-employment, if the employment or self-employment is pursued in only one Member State;
2. the legislation of the Member State of residence where the person concerned performs part of his activity/activities or where the person is not employed or self-employed;
3. the legislation of the Member State the application of which was first requested where the person pursues an activity or activities in two or more Member States.

If one month after the divergence arose the competent institutions cannot reach an agreement, the matter may be referred to the Administrative Commission for the Coordination of Social Security Systems, which seeks to reconcile the positions within six months (Article 6(3) of Regulation 987/2009).

If it is established that the applicable legislation is not that of the State provisionally identified, the institution found to be competent is considered so retroactively, as if no divergence had ever existed (Article 6(4) of Regulation 987/2009).

Upon request of the institution identified as competent- submitted within three months – the institution that collected contributions provisionally must transfer them to the competent institution (Articles 6(5) and 73 of Regulation 987/2009).

The competent institution of the Member State whose legislation becomes applicable must inform the person concerned and, if applicable, their employer(s), of the obligations under that legislation (Articles 16(5) and 19(1) of Regulation 987/2009).

3. A1 Certificate and Its Binding Nature

As noted, the process of identifying the applicable social security legislation may be more or less swift depending on whether disputes arise between the institutions involved.
The outcome of this process is reflected in the A1 Certificate, which certifies the sole applicable social security legislation.

However, it may occur that during INPS inspections – despite the fact that workers hold a valid A1 Certificate attesting subjection to the legislation of another Member State – INPS may nonetheless order contribution regularization, demanding payment of omitted contributions and related penalties.

This raises the question: what is the legal value of the A1 Certificate issued by the competent institution of the issuing State, and can other Member States challenge or ignore it?
The answer lies in Article 5 of Regulation 987/2009, titled "Legal Value of Documents and Certificates Issued by Another Member State", which provides:
"Documents issued by the institution of a Member State and showing the position of a person for the purposes of the applica tion of the basic Regulation and of the implementing Regulation, and supporting evidence on the basis of which the documents have been issued, shall be accepted by the institutions of the other Member States for as long as they have not been withdrawn or declared to be invalid by the Member State in which they were issued".

Article 5 sets out a procedure to follow when the institution receiving the document doubts its validity or the accuracy of its underlying facts.
This procedure includes:
– requesting clarification and, if necessary, withdrawal;
– re-examination by the issuing institution;
– verification by the institution of the person's State of residence;
– possible referral to the Administrative Commission if no agreement is reached.
This procedure implements the principle of cooperation under Article 76 of Regulation 883/2004, which imposes reciprocal obligations of information and assistance.

Jurisprudential Principles on the Binding Nature of the Certificate (A1 / Former E101)

The binding nature of A1 Certificates derives from well-established case law of the Court of Justice of the EU, originally developed under the previous Regulations (No. 1408/71 and No. 574/72) concerning Certificate E101.
Key judgments include:

– CRPNPAC v. Vueling Airlines SA (C-370/17 & C-37/18), 2 April 2020
The Court held that:
– Even in the presence of indications of fraud, the host State's authorities and courts cannot unilaterally disregard the certificate.
– The certificate creates a presumption of regularity and is binding until withdrawn or invalidated by the issuing institution.
– Host State authorities must initiate the cooperation procedure, not act unilaterally.
– Ignoring the certificate risks:
" violation of the principle of a single applicable legislation,
" double contributions,
" uncertainty and unpredictability for employers and workers.
The Court clarified that only after the cooperation procedure has been duly followed, and the issuing institution fails to act within a reasonable period, may a national court disregard the certificate.

– Fu (C-410/21 & C-661/21), 2 March 2023
– The Court reaffirmed that:
– The issuing institution may revoke an A1 Certificate only after re-examining the grounds for issuing it within the context of the cooperation procedure.
– Allowing the certificate to be deprived of effect outside that procedure would undermine legal certainty and the principle of loyal cooperation.

Zakład (C-422/22), 16 November 2023
The Court clarified that:
– If the issuing institution itself decides to revoke the A1 Certificate on its own initiative (not upon request of another State), the cooperation procedure is not mandatory, as no inter-institutional dispute exists.

" Ex (C-421/23), 23 January 2025
The Court held that:
– Regulation 883/2004 applies even when A1 Certificates are falsified.
– Falsity does not automatically exclude application of the Regulation.
– National courts must still determine the applicable legislation based on the Regulation's criteria.
– The cooperation and conciliation procedure remains essential for disputes concerning certificate validity or authenticity.

4. Conclusions

In light of EU legislation and the evolving case law of the Court of Justice, it is clear that INPS and national courts – as well as all social security institutions and courts of EU Member States – cannot order the payment of contributions to INPS where a valid A1 Certificate attests that another Member State's social security legislation applies.
A1 Certificate is binding for all Member States.
Its arbitrary disregard implies:
– a violation of the principle of loyal cooperation between Member States,
– a breach of the principle of the uniqueness of the applicable legislation, and
– an obstacle to the free movement of workers.

Originally published 7 November 2025

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