The German Ministry of Employment and Social Affairs has issued guidance stating that, it its view, there is no European law duty to carry an A1 certificate on short-term business trips between EU/EEA countries and Switzerland.
However, according to the Ministry, member states can exercise their discretion to put an A1 certificate requirement in place through national law (currently France and, in principle, Austria have done so). Carrying an A1 certificate is recommended in these states. For business trips to Germany, there is no duty to carry an A1 certificate under German national law.
This guidance is not binding for other EU or EEA member states and Switzerland, therefore other states can interpret EU law to mean that carrying an A1 certificate is mandatory. Not carrying an A1 certificate on business travel therefore still poses risks.