In principle, no work permit requirement exists in the case of a transnational service provided for up to 8 (eight) days per calendar year. However, a visa may be required for entry. Please check the applicable visa provisions.
If you are an employee of a company that has its registered office in an EUEFTA state, your employer can second you to Switzerland for up to 90 days per calendar year without a work visa, providing that you have previously been integrated long-term in the regular labour market of an EU or EFTA member state (i.e. you have held a temporary or permanent residence permit for at least 12 months). The placement in Switzerland must be notified to the authorities according to a specific procedure.
For any stay of more than 90 days within any 180-day period, nationals of countries other than EU or EFTA member states must apply for a national visa/residence permit, which can be awarded together with a work permit. In most cases, applications must be made before arriving in the country.
In Switzerland, employers are responsible for obtaining work permits. They submit the application along with the necessary documents to the labour market or migration authorities in the relevant canton. These authorities provide information about the procedure and the application documents to be submitted. The full procedure can be found here.
Here are the contact details of the cantonal immigration and employment market authorities.