Foreign Posted Workers on US Sites: Certificate Cross-Checks

The A1 certificate is a European document; it does not exist in the United States. The US counterpart for workers sent temporarily from a partner country is the certificate of coverage issued under a Social Security totalization agreement. Checking the documents of a foreign worker on a US construction site therefore means comparing four sources: the certificate of coverage from the sending country, the identity and work-authorization documents, the employment contract, and payroll records. Each can be valid on its own and still fail the comparison: a certificate that ends before the project does, an employer name that differs from the contract, a worker on site who is not on the roster. This article describes what each check compares and what the reviewer does next. It does not claim that a check proves a document is authentic.

Rules are described as of 5 November 2026 and change; confirm them with the agencies linked. This is general information, not legal advice.

What does the certificate of coverage establish?

Under a totalization agreement, a worker temporarily transferred to work for the same employer in another country generally remains covered only by the country that sent them. The IRS explains this detached-worker rule and notes that the certificate serves as proof of exemption from the other country's system. Limits on duration vary by agreement, so read the text of the specific agreement rather than relying on a general figure.

For an inbound worker, the certificate is issued by the sending country's institution, not by a US agency. The reviewer therefore compares what the document says with what the contract and roster say, and asks the employer to obtain a corrected version from the issuing institution when they differ. The US side of the process, for American workers sent abroad, runs through the Social Security Administration. A US reviewer should not assume that a foreign certificate carries the same layout as the European A1.

No US federal "posting declaration" equivalent to the European prior notification was verified for this article, and state rules differ. We therefore make no claim about one. What follows is the generic comparison.

What does each document prove, and what does it not?

Each document answers one question, and none replaces the others.

If your company is the employer of record in the US, Form I-9 obligations apply to you. If the worker is employed by a foreign subcontractor, who must complete what is a legal question to put to counsel; the cross-check below works either way.

Which fields should be compared?

Seven comparisons catch most mismatches on a US site.

A spelling variant and an expired certificate do not carry the same weight. Log the gap, the answer and the access decision each time.

How long can a temporary assignment run?

The duration depends on the totalization agreement in question, so there is no single number. Some agreements allow assignments of several years; others are shorter. Sources describing the US rules give differing figures for specific countries, which is why the agreement text and the issuing institution are the references. The useful cross-check is cumulative time on US projects, successive sites included, against the period printed on the certificate.

What do site managers actually ask?

"Does the certificate let someone start work?" No. It addresses social security only. Work authorization and site credentials are separate checks.

"The certificate arrives after the worker has started. Now what?" Log the delay, request the document, and decide internally whether access continues in the meantime. No rule makes that decision for you; set the cut-off date in the subcontract.

"Does a clean I-9 mean the paperwork is consistent?" No. It speaks to identity and work authorization. Employer name and period on the certificate still need to be matched against the contract.

Where does automation help?

On a project with several subcontractors the table above becomes dozens of comparisons per company. A document-validation tool compares names, birth dates, employer and validity dates across the documents in one file and flags the gaps, with a log of what was checked and when. It shows where documents disagree; it does not say whether a document is genuine. Handling of personal data in these files is also a state-law question; US privacy rules are set mostly at state level (CCPA in California, for instance), so involve counsel before you centralize copies of identity documents.

The construction solution page explains what CheckFile compares in a subcontractor file; see also security and pricing.

Related reading: subcontractor compliance documents in construction and the industry verification guide.

Frequently Asked Questions

Is there a US version of the A1 certificate?

The closest equivalent is the certificate of coverage under a totalization agreement. It plays the same role for social security, but each agreement has its own terms and duration limits, so read the agreement for the country concerned.

Can a general contractor reject a certificate it finds suspicious?

It cannot invalidate a foreign certificate itself. It can record the mismatch, ask the employer for an explanation or a corrected document, and take legal advice if the doubt remains.

Does Form I-9 replace a certificate of coverage?

No. Form I-9 concerns identity and work authorization; the certificate concerns which country's social security system applies. They answer different questions.

What should be compared first?

Name and date of birth on the certificate against the passport, then the employer on the certificate against the contract, then the validity period against the project schedule.

Does an automated check prove a document is genuine?

No. It compares fields across documents and flags inconsistencies; authenticity rests with the institution that issued the document.