Did one of the most powerful Republicans in Washington break federal law? That’s the question the Citizens for Responsibility and Ethics in Washington is hoping to answer, leading the watchdog group to file a complaint asking the Senate Select Committee on Ethics to investigate whether McConnell may have illegally used congressional staff time or resources for his reelection campaign.

CREW filed the complaint in response to campaign strategy meetings disclosed this week in secretly taped session.

“If Senator McConnell was misusing his office staff–who are paid for by our tax dollars–to engage in campaign work, that’s a violation of a Federal criminal law and Senate ethics rules and he should be held accountable for that,” the group’s Executive Director Melanie Sloan said on Thursday’s PoliticsNation.

The leaked recording seems to reveal that legislative aides helped to gather opposition research against possible challengers including Ashley Judd, who’s since announced she won’t run, and Kentucky Secretary of State Alison Lundergan Grimes. These staffers are permitted to work on campaigns during their free time, but not on the taxpayer dime, and breaking that rule would be an ethics violation.

CREW is focused on two people referred to by name on the tape, a Phil Maxson, who’s a legislative aid, and a Josh, who may be Josh Holmes. “Neither one of those people has been paid by his campaign committee, we checked the Federal Election Commission reports, but they both are on Senate staff,” says Sloan.

Sloan describes it as “unusual” for legislative aides rather than campaign staff to engage in opposition research. “It’s true that those aides could do this if that was on their free time, but they were spending a lot of time on this,” she said.

McConnell’s staff already called for an FBI investigation into how the recordings were obtained, complaining that he was subject to “Nixonian” style attacks. Sloan says the FBI should broaden its investigation to the content of the recording.

“Senator McConnell has been anxious for there to be an FBI investigation into this entire matter, and he’s got one, the FBI has started looking at it,” she said. “A full, thorough, and fair investigation would also look at whether Senator McConnell broke the law.”