There was a guy at my work who regularly took his shoes and socks off in the canteen to rub his feet. It took at least 3 meetings with HR and a 'stop doing that or you're fired' final letter. He then left the business of his own accord.
Just saying, keep your feet covered is a valid position to take in a professional situation.
interesting professional surrounding you have, Anroth. Really, you have to be a high lever employer with such colleges. But tell me something more about you other colleges and the medical supervisors and the rest of the team if you want. Because is interesting, in Holland we have about the same, something similar, the Sociale Werkvoorziening.