Fine upset corporation importing chlorine (5)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

CL in TUM (a crossword favourite, where corporation means stomach) all reversed. Not a very common word; it means to cheat or defraud, to fine, or a fine. I blithely biffed the clue and thought MULCT was mulch, without writing in mulch – if you follow what I mean.