Combating undeclared work: A1 certificates required for EU/EEA staff travelling abroad
Employees of employers in Germany must carry an A1 certificate for each activity carried out in another EU country (EU, EEA and Switzerland). This also applies if it is only a one-day business trip and may concern participation in a trade fair, a visit to a customer, cooperation partner, the head office of the employer or affiliated companies abroad.
Here you can read more!