If you are hired and start working with dreadlocks or long hair in general in the food service industry can the manager then require you to cut them to keep your job?

AnswerYour manager is entitled to change the policy at any time, especially in matters of health. You should be given reasonable time to make whatever changes as are necessary, but remember... you are working for someone else.

not with dreadlocks that would be religious discrimination and illegal

you do not have to be rasta to claim religious connection to dreading

No. As long as you keep your appearance neat and clean they cannot tell you to cut your long hair.