But some air marshals, in interviews and internal communications shared with the Globe, say the program has them tasked with shadowing travelers who appear to pose no real threat — a businesswoman who happened to have traveled through a Mideast hot spot, in one case; a Southwest Airlines flight attendant, in another; a fellow federal law enforcement officer, in a third.

It is a time-consuming and costly assignment, they say, which saps their ability to do more vital law enforcement work.