No there aint any such restrictions..
I myself have been working in an audit firm as an intern from past 8 months. And i am still doing my fundamental papers and havent even completed my graduation yet.
I dont think so that this is a restriction. I personally judged and also watched that students in F Level are doing jobs BUT students of the professional papers ALMOST performing some roles in the industry and also in the firm.
But if you are in the professional papers you should start doing some job.AS I personally searching job for my self but for 1 year I still didn't find a job.
Hope that you got the point..