Discipline Press covering Ulster (6)
I believe the answer is:
punish
'discipline' is the definition.
(thesaurus)
'press covering ulster' is the wordplay.
'press' becomes 'push' (pushing is a kind of pressing).
'covering' indicates putting letters inside.
'ulster' becomes 'ni' (Northern Ireland).
'push' enclosing 'ni' is 'PUNISH'.
(Other definitions for punish that I've seen before include "Fine perhaps" , "Cause to suffer for an offence" , "Treat harshly or severely" , "Flog" , "Chastise" .)