Questions about the influence of lobbyist spouses have confounded lawmakers for decades, and now confront the House Ethics Committee as it probes whether Kentucky Republican Edward Whitfield broke rules because of his staff’s work with his lobbyist wife.

The Ethics panel may have to guess at the answer. House rules bar a lobbyist married to a House member from “lobbying contact” with any member of that lawmaker’s staff. But that phrase is open to interpretation.

Whitfield’s staff set up dozens of meetings for his wife on Capitol Hill, according to the Office of Congressional Ethics. The office also said she urged Whitfield to take specific actions. Whitfield dismissed the allegations.

Not everyone agrees what defines the lobbying contact addressed by House rules.  Beyond a few paragraphs urging “special caution” when members have lobbyist family members, the exact parameters of what’s permitted in the House remain hazy.

The Ethics Committee acknowledged as much when it formed a bipartisan working group in 2013 to review its guidance regarding conflict-of-interest rules, and to recommend clarifications.

Headed by Reps. Susan W. Brooks, R-Ind., and Ted Deutch, D-Fla., the working group met two dozen times in 2013 and 2014, and last year recommended that House members disclose holdings in such complicated investment vehicles as hedge funds. The Ethics panel has since issued new guidelines for investment disclosures.

But the working group appears to have taken no action on the broader and more complicated issue of conflicts of interest, whether they involve lobbyist spouses or official actions that may enrich a member. Asked whether the working group is still meeting, an Ethics Committee spokesman declined to comment.

The absence of clear, robust conflict-of-interest rules poses both risks and temptations for a long list of lawmakers with lobbyist family members, including spouses, parents, children, nieces, nephews and in-laws.

Data is scant, but a 2014 report by Citizens for Responsibility and Ethics in Washington identified 30 senators who have family members who lobby or work in government affairs. The most recent House data is from 2012, when a CREW report found 44 members who have family members working as registered lobbyists or in government relations.

Both the House and the Senate tightened ethics rules following the 2006 Jack Abramoff scandal, which turned up so many lobbyist spouses that FBI investigators reportedly dubbed them “the Wives Club.” Among others, the spouses of then-Reps. John Doolittle, R-Calif., and Tom Delay, the former GOP majority leader from Texas, had worked for Abramoff directly or indirectly.

The Senate’s rules are tougher than the House’s because they bar any immediate family member of a senator from lobbying contact with any Senate office.

The House’s lobbying restriction should be expanded from covering the spouse and staff to the entire chamber, and it should include all immediate family members, said Craig Holman, government affairs lobbyist for Public Citizen.

The ethics pitfalls of lawmaker-lobbyist marriages are not new. As early as 2001, then-Rep. Jim Nussle, R-Iowa, consulted the Ethics panel on how to avoid the appearance of impropriety before marrying his lobbyist wife. Nussle now runs his own lobbying firm.

In 2004, controversies over lobbying by Linda Daschle, the wife of then-Senate Minority Leader Tom Daschle, D-S.D., prompted Nevada’s Harry Reid, now the minority leader himself, to propose lobbying curbs for congressional family members.

In Whitfield’s case, the Ethics Committee is probing contacts between the congressman’s staff and his wife, Constance Harriman Whitfield, a lobbyist for the Humane Society Legislative Fund. The Office of Congressional Ethics, which reported on the meetings Whitfield’s staff set up, uncovered the details in a preliminary investigation.

The ethics office report points to emails from Whitfield’s wife that show she requested a meeting with another lawmaker; made requests about the specific language in legislation, and urged that Whitfield take specific action with regard to certain statements, letters or votes.

Whitfield has called the allegations “absurd,” and noted that one of the bills at issue, his Prevent All Soring Tactics Act, involves a matter that he has “followed for many years.”

Soring is a tactic that forces horses into an exaggerated gait by manipulating their legs and hooves. Whitfield also said the parties that lodged the ethics complaint are representatives of the Tennessee walking horse industry who have collectively violated the Horse Protection Act 57 times.

Whitfield’s attorneys have said Whitfield’s wife is “a trusted confidante of her husband and one of his most important personal and political advisers.”

Invariably, the line between marital confidant and influence professional will be fuzzy.

“Sometimes it’s hard to regulate morality — you’re either moral or you’re not,” said Craig Engle, a partner specializing in political law at Arent Fox. “But in this particular case, you are going to have to try to regulate morality. And I think it’s up to Congress to write rules for themselves that are clear.”