Before the posting begins, the employer must notify the designated cantonal authority online and in the official language of the posting location.
More information can be found on the following link :
https://www.sem.admin.ch/sem/en/home/themen/fza_schweiz-eu-efta/meldeverfahren.html
The notification must be made at least eight days before the work starts. The cantonal authority will then forward a copy of the notification to the cantonal tripartite commission and, if applicable, to the joint commission established by the extended collective labor agreement.
Here are the contact details of the cantonal immigration and employment market authorities.
If a service is to be performed in multiple cantons, the request must be made to the cantonal authority of the canton where the activity will be the longest.