Washington (CNN) At least one Republican senator will join with Democrats on a bill that would reverse the Trump administration's plan to ease sanctions on three companies with ties to Russian oligarch Oleg Deripaska , a close Kremlin ally.

"I anticipate voting to overturn the decision by the administration," Sen. Cory Gardner, a Colorado Republican, told reporters Tuesday.

A key vote on the measure, which Minority Leader Chuck Schumer can force under the 2017 Russia sanctions law, is expected later in the day and will give Democrats another chance to blast Republicans over President Donald Trump's relationship with Russian President Vladimir Putin.

Only four Republicans need to break with their party to advance the measure, if all Democrats vote to do the same.

Growing potential for Republican defections comes amid a new wave of questions about Trump's relationship with Putin in the wake of a bombshell New York Times report that the FBI in 2017 decided to investigate why Trump took actions that seemed to benefit Russia

Treasury Secretary Steven Mnuchin briefed Senate Republicans at their weekly policy lunch and address their questions about why the administration moved to lift the sanctions.

"This shouldn't be a political issue," Mnuchin told reporters after the lunch. "This is an issue of great importance." He noted the sanctions decision, which doesn't apply to Deripaska personally, was reached following "a long negotiation."

Congress faces a Thursday deadline to halt Treasury's move to lift sanctions on three entities: Rusal, the world's second-largest aluminum producer, as well as EN+ Group and JSC EuroSibEnergo.

Republicans expressed concern heading into the vote.

"We're listening to our members and obviously want to listen to the arguments that the administration is making," Sen. John Thune, who as whip is the second-ranking member of GOP leadership, said Monday night. "We are at this point gathering feedback."

Thune acknowledged it could be difficult for some Republicans to vote against the measure because it could be viewed as a pro-Russian or pro-oligarch move.

"I think there is a lot of that swirl around the issue. And sometimes the facts can be very different than what the perception of it might be," Thune said. "The fact pattern here is one we're trying to get to the bottom of, and we're going to hear from the administration and let them make their best argument. But I think our members have some questions.

Sen. Shelley Moore Capitol, R-West Virginia, said Monday night she was still learning details of the bill but recognized its potential downsides for GOP senators.

"My understanding is that the easing of sanctions on a spurious character is questionable," Capito said.

Sen. Rob Portman, R-Ohio, also said Monday night he would need to study the bill while saying that he generally supports tough sanctions on the Russians.

"I need to take a look at it. As you know, I've been outspoken on the sanctions because of the concerns I have over the Ukraine, and Syria and other issues, so I'd be more on that side," Portman said.

If the bill advances on a simple majority vote, it could face a higher 60 vote threshold to overcome a filibuster possibly later this week. That would be a bigger challenge for Democrats because they would need the support of 13 Republicans.

A spokesman for Senate Majority Leader Mitch McConnell declined to comment on the push by Schumer, who said over the weekend he would move ahead with a vote under a 2017 law that gave Treasury new powers to go after Russian oligarchs in order to punish the Kremlin for interfering in the 2016 election.

The law also gave Congress the authority to disapprove any decisions by the Trump administration to weaken sanctions, providing lawmakers with a 30-day window to reject the plan if it undermines US economic and national security interests.

Treasury notified Congress in mid-December of its intent to lift sanctions on those firms following "significant restructuring and corporate governance changes" including reducing Deripaska's both direct and indirect stake in the companies. Sanctions will still remain on the Russian oligarch, however.

Those firms were swept up as part of more than 200 sanctions imposed on Russian targets in April by Treasury, including on Deripaska and his entire business empire to prevent him and his companies from using the US dollar and doing business with US citizens. The companies have spent nearly eight months negotiating with Treasury how to significantly reduce Deripaska's influence in order to have sanctions lifted.

US ambassadors to the UK, France, Germany and the European Union also wrote a joint letter to Schumer and House Foreign Affairs Chairman Eliot Engel last week urging for sanctions to be lifted on the three firms. They argued Treasury's decision would help to "safeguard" more than 75,000 workers jobs across Europe's aluminum industry.

Some senior Republicans said they planned to vote no on the Democratic bill, siding with Treasury on lifting sanctions.

Sen. James Lankford, an Oklahoma Republican, said he will oppose the resolution because the companies abided by the rules that were established in the 2017 Russia sanctions law about majority ownership in companies.

"This vote now is about actually saying 'just kidding' — they went through all the process to make sure that Deripaska was not a majority owner," Lankford told CNN. "They're abiding by the law, and they're having a conversation to do sanctions on them anyway. That to me is a problem long term. Now I'm no fan of Oleg Deripaska, he's a scoundrel, but we either pass a law and abide by the law we pass or not."

Senate Finance Chairman Chuck Grassley also said he would reject the Democratic resolution because the company met the conditions of majority ownership.

"I'm going to vote no because the company and the individual are separate," Grassley said. "He did it, so the condition on putting sanctions on the company are no longer valid."

House Majority Leader Steny Hoyer, the second-ranking Democrat, introduced a parallel resolution on Tuesday, giving the House the option to proceed ahead of Thursday's congressional review deadline.

Last week, after Mnuchin briefed House members, Speaker Nancy Pelosi described the classified meeting as a "waste of time." When asked if she would consider a resolution of disapproval to block the removal of sanctions, Pelosi said, "We'll see."

Mnuchin has denied the move to lift sanctions was intended to help the Kremlin, telling reporters the Treasury Department's decision to lift restrictions on companies tied to Deripaska was "not politically motivated."

"Treasury has made its best judgment for applying the law and regulations for us to have effective sanctions programs," Mnuchin told reporters after the classified House briefing. "We both have to have a way that companies that are affected by ownership and control will be picked up and then a fair way that they'll be delisted."

He said would consider potentially extending the statutory 30-day deadline, but no firm decision has yet been made, according to a Treasury spokesman.

It's not the first time Mnuchin has been caught having to explain a controversial move by the Trump administration, including a decision to maintain close relations with Saudi Arabia following the murder of dissident journalist Jamal Khashoggi.

Trump has insisted the new report from the New York Times that the FBI launched a probe to look into whether he took actions that seemed to benefit Russia is a "hoax."

"I never worked for Russia," Trump told reporters on Monday as he was departing for an event in New Orleans. "Not only did I never work for Russia, I think it's a disgrace that you even asked that question because it's a whole big fat hoax. It's just a hoax."

Trump also derided the FBI officials who launched the probe as "known scoundrels" and "dirty cops," while standing by his decision to fire Comey despite broader ramifications on the special counsel's investigation.

"I just don't know anything about it," he said, before insisting that one-on-one meetings with foreign leaders were routine and not nefarious.

"We have those meetings all the time," Trump said. "No big deal."

CORRECTION: This story has been updated to reflect Rep. Steny Hoyer's current position.