A number of Senate candidates have not cut their ties to companies with vested interests in legislation the contenders could be voting on, should they be elected.

Former Wisconsin Gov. Tommy Thompson (R); former Sen. George Allen (R-Va.); former U.S. Surgeon General Richard Carmona (D), who’s running in Arizona; and former North Dakota Attorney General Heidi HeitkampHeidi HeitkampSenate Democrats: ObamaCare repeal fight isn't over yet Dem senator: Don't bet against McConnell on ObamaCare repeal Senate Dem undecided on 2018 reelection run MORE (D) have all retained positions on boards of companies that could be affected by legislation brought up in Congress.

All four previously held roles in government, and many of their current jobs are based on the expertise they accrued while in those positions. Thompson, who is also a former Health and Human Services secretary, still advises more than a half-dozen healthcare companies. Carmona also has ties to a number of companies, while Allen remains the owner of a Beltway-based government consulting firm and Heitkamp works for a North Dakota-based energy company.

“It’s commonplace, but that doesn’t mean these aren’t real concerns, and they’re something that should be weighed very seriously,” said Meredith McGehee, the policy director of the Campaign Legal Center, a government watchdog group. “It’s not disqualifying and it’s not necessarily a conflict, but that’s for voters to gauge.”

Senate ethics rules apply only to sitting senators, not candidates. The rules state that members may not serve as an officer or member of the board of any publicly held or -regulated company. Candidates aren’t constrained by those rules but would have to resign their positions on boards should they win on Election Day.

According to a review of recently filed Exchange Commission filings and his personal financial disclosure statement, Thompson remains on the board of Centene Corp., which runs Medicaid in a number of states and was paid for serving on the boards of companies involved in medical supplies or pharmaceuticals including CR Bard, Cytori Therapeutics and United Therapeutics, earning him nearly $300,000 last year. Thompson has promised to push to repeal Democrats’ healthcare reform law, which could have a major impact on those companies.

Thompson’s opponent, Rep. Tammy BaldwinTammy BaldwinMajor progressive group rolls out first incumbent House endorsement Dems push for more action on power grid cybersecurity Overnight Regulation: Labor groups fear rollback of Obama worker protection rule | Trump regs czar advances in Senate | New FCC enforcement chief MORE (D-Wis.), has attacked him for his private-sector work, saying in a recent ad that he cut “sweetheart deals with drug companies” while in office, then earned “millions in a D.C. lobbying firm working for drug companies.” 

He and Baldwin are neck and neck in the polls.

“I’ll be ready to resign them tomorrow if I win,” he told The Hill last week when asked about the board positions.

“His private-sector work was all fully disclosed, vetted and extensively reported on earlier this year,” Thompson spokeswoman Lisa Boothe told The Hill. “The governor is not an elected official and is currently working in the private sector creating jobs.”

Heitkamp has kept her job on the board of the Dakota Gasification Co. — and routinely touts that work on the campaign trail to put distance between herself and President Obama on energy policy. She earned $20,000 from them last year, according to her personal financial disclosure form.

“Heidi’s extensive private-sector experience in the energy sector makes her uniquely positioned to make sure the Keystone pipeline gets built and that we protect North Dakota jobs not only in the oil, gas and coal industries, but the wind industry as well,” said Heitkamp spokesman Brandon Lorenz when asked about the position. “Heidi will put North Dakota first and comply with all appropriate Senate ethics rules to avoid potential conflicts of interest.”

Her opponent, Rep. Rick Berg (R-N.D.), has not made a campaign issue of her ties to energy companies — but has slammed her for receiving contributions from environmental lawyers, a sign that her spot on the board doesn’t hurt her in the energy-producing state. The two are locked in a tight race.

Heitkamp is also on the board of Abrams Learning and Information Systems, a Virginia-based consulting firm focused on homeland security issues. Lorenz pointed out that retired Gen. John Abrams, the company’s owner, wrote a glowing endorsement of her in an op-ed published last week in the Grand Forks Herald. 

Allen earned $350,000 last year from George Allen Strategies, a Beltway-based firm he launched after he lost his Senate reelection bid in 2006 that employs a former Allen staffer who is a registered lobbyist.

“Clients of Gov. Allen’s firm have already been properly disclosed on his personal financial disclosure statements that have been publicly filed with the U.S. Senate. If elected to the U.S. Senate, George Allen Strategies will no longer be in operation,” said Allen spokeswoman Katie Wright when asked about which clients Allen’s company is currently advising. The forms were filed in May.

Allen and former Virginia Gov. Tim KaineTim KaineLawmakers wary of Trump escalation in Syria Va. Republicans to choose challenger to Tim Kaine through primary Live coverage: Senate Dems hold talkathon to protest GOP health plan MORE (D) are locked in a tight race. 

Carmona, who has a background in the military and law enforcement as well as healthcare, has retained positions on the boards of Healthline Networks, an online healthcare information service partly owned by insurance giant Aetna. He’s also on the board of the Clorox Co. and Taser International, the stun-gun manufacturer, and sits on the scientific advisory board of Schiff Nutrition International, which makes vitamins and supplements. Those positions earned him a combined $170,000 last year.

Carmona and Rep. Jeff FlakeJeff FlakeOPINION: ObamaCare by another name is still ObamaCare Senate should seek to retain its 'blue slip' tradition for judicial nominees Progressives target Heller and Flake on Senate GOP bill MORE (R-Ariz.) are in a close race for Arizona’s open Senate seat. His campaign did not respond to requests for comment. Flake hasn’t raised any of the board positions as a campaign issue.