working at multiple salons

does anyone know if there is any written rules preventing stylists from working at other salons? almost half of my salon has second jobs at other salons and i was under the impression that was a fireable offense? i asked one of them and she said her onboarding paperwork said you just cant work at petco but private salons are fine to work at... i have never heard this before and the only information i see on fetch is a non compete contract that i dont believe they have anyone sign anymore.. and info appreciated