20% is fine for a haircut. It's perfectly acceptable.
In fact, we all should stop to frequent places that exploit employees by not paying them a livable wage. And if the solution to this means an increase in price, so be it.
The defense of 'they might be contractors', which rent a seat for a fixed price or on a % revenue sharing with the salon is even more ridiculous.
They are contractors, so they have all the means to set their own price.
My barber and most in the area have increased their prices significantly. 20% at $20 isn't bad. When my haircut is now pushing 35-40 range it becomes harder to stomach.