This is an event (coming under fire) which started in the past and still continues or has an impact in the present.

Thanks Cheska :) Happily there's no one to assign me homework because I'm myself an English teacher :P I have just one more question. I can't exactly see why the present perfect tense was used in the sentence. In fact, to me, the whole problem lies in that part.

As medical costs soar, the philosophy underlying physical check-ups has come under fire as it is both a waste of time and money. Good homework ;)