This has been my experience. One employer tried. With the help of a labor attorney, I told them that if they wanted to enforce the clause then I would voluntari

This has been my experience. One employer tried. With the help of a labor attorney, I told them that if they wanted to enforce the clause then I would voluntarily withdraw my acceptance of a new job offer and then avail myself of the courts. Burned a bridge, of course, but it took them about 20 minutes to decide I wasn't worth the hassle.