How are non-competition employment agreements legally binding?

Some employers compel employees to sign forms which say you agree not to work for similar businesses within a certain distance (5 miles) and/or time (2 years) of the time/place of employments. The one I’m looking at says that “violation of the terms… will result in legal action.”
There is no penalty specified. So, what would the potential legal action be? Seems to me the best they could do would be to use it for grounds to terminate your employment if they so chose.
Also seems like bullying that shouldn’t really be legal, and that it would limit one’s freedom to pursue happiness (i.e. unconstitutional).
The types of work I have seen for something like this have included administrative office work, and working as an instructor in a health club.
This is in Washington State (USA).