"In exchange for a salary, they promised not to work for anyone else." Is that legal? It's certainly not 'the market' at work, or working well, but simply corp

"In exchange for a salary, they promised not to work for anyone else." Is that legal? It's certainly not 'the market' at work, or working well, but simply corporations monopolizing peoples productive hours, even those not actually part of the job, with an 'exclusive contract'. 'Employment' is a bit of a racket IMHO, so any way of getting out from under the thumb should be encouraged.