Hi Rufio. The salary information is used to determine your credit limit. While you are required to specify an employer, there is very little chance of them contacting your employer. More commonly, the issuer will ask you for a copy of your recent bank account statements to check that you are receiving a salary from the stated employer.
When you apply, the issuer will also check your ZEK record to find out if you have existing debt or if you have defaulted on loans in the past. If there is a risk that granting you a line of credit could result in your becoming over-indebted (having more debt than you can actually service) then your application will be denied. They may also check your municipal debt collection register. If you have never taken out loans or failed to pay bills in Switzerland, you won’t likely have any credit history. This is considered a positive because only negative and neutral information is recorded (not positive credit behavior like in the US).