Mesira if required by government?

 Igros Moshe (C.M. 1:92): Is it permitted to take a job as a government financial auditor when there are times when he will find fraud and therefore he would have to inform (moser) on the transgressor to the government which will punish the tax cheat more than the proscribed by the Torah? Yes it is permitted since the job of government auditor is to find transgressions. It is clear however that if this person did not accept the job there will obviously be others to take the job and they will find the transgressions. Consequently the transgressor suffers the same loss  whether this person takes the job or not or someone else takes the job and he doesn’t cause him any harm.. Therefore if no one is actually harmed by his taking the job it isn’t relevant to prohibit taking the job…. And this is exactly our case when the government orders someone to bring their account books to be examined by an auditor because the government already controls the situation to find his fraud and will find it through any one of their auditors. Therefore this is another reason for exempting any particular auditor when they find fraud…. And even if they don’t force him to testify but he is required to testify about the fraud because this is like the case of someone designated to testify for a non‑Jews and he is fact required because of chillul hashem that would result if he didn’t testify. This is the accepted  halacha (C.M. 28:3)