I'm working on a fixed rate contract and we have already defined payment dates on the contract. The thing is, the client will be two weeks late of scheduled payment date for some confidential reason. Should I add a late payment fee or penalty so that next time, I will get my pay on time?

I'm working on a fixed rate contract and we have already defined payment dates on the contract. The thing is, the client will be two weeks late of scheduled payment date for some confidential reason. Should I add a late payment fee or penalty so that next time, I will get my pay on time?