(BOSTON) — TAMPA, Fla.—Mitt Romney launched a multipronged attack Monday on rival Newt Gingrich, including a scathing TV ad and personally accusing the former House speaker of engaging in “potentially wrongful activity” in his consulting work over the past decade.

Romney called on Gingrich to release his client list for that period. He offered no proof that Gingrich had engaged in wrongful behavior when, after leaving Congress, he worked with former colleagues to push for a prescription drug benefit for Medicare. Gingrich has never been a registered lobbyist.

“Was he working or were his entities working with any health care companies that could’ve benefited from that? That could represent not just evidence of lobbying but potentially wrongful activity of some kind,” Romney told reporters after a campaign appearance.

Note: Read our discussion guidelines before commenting.