Such agreements would typically apply to all actions, not just class action.
Ie you get fired unjustly, instead of suing you have to use binding arbitration. Which typically tends to favor the employer. Also the major reason employers prefer this is because an emotional case before a jury can result in huge awards all out of proportion to the actual damages. With arbitration, the best the employee can get is the actual damages (pain and suffering might be an option in some cases, but no huge windfalls).