> In USA, even minimum salary for servers is lover then minimum salary for other workers - the law expects the tips.

Not true. The federal minimum wage for servers and other tipped employees is the same as other employees: it's just the minimum wage.

https://www.dol.gov/whd/regs/compliance/whdfs15.htm

"Where an employee does not receive sufficient tips to make up the difference between the direct (or cash) wage payment (which must be at least $2.13 per hour) and the minimum wage, the employer must make up the difference."

Interesting, they did not told us that part when I worked in USA in summer. Cooks got 6.5$ and that was minimum wage in there. Servers got 1.5$ and had to report all tips to be taxed. Then again, servers earned more overall, so minimum wage was not really an issue for them.

Literally the third sentence in your link provides support for GP's position:

"The employer is prohibited from using an employee’s tips for any reason other than as a credit against its minimum wage obligation to the employee (“tip credit”)"

You are mistaken. Please read the rest of the article, and the comment that is a peer to yours.

"Where an employee does not receive sufficient tips to make up the difference between the direct (or cash) wage payment (which must be at least $2.13 per hour) and the minimum wage, the employer must make up the difference."