Congressional leaders are acting to force the Obama administration to confront Russia on its violations of a nuclear treaty that U.S. officials have acknowledged since 2012.

On November 27 of that year, two top Obama administration officials held a closed-door hearing with the Senate Foreign Relations Committee, chaired by Sen. John Kerry, who only months later would become President Obama’s secretary of state. Inside the top-secret hearing, acting Undersecretary of State for Arms Control and International Security Rose Gottemoeller and Assistant Secretary of Defense for Global Strategic Affairs Madelyn Creedon told lawmakers that Russia had violated the 1987 Intermediate-Range Nuclear Forces Treaty (INF), according to two U.S. officials who attended the classified meeting.

Inside the meeting, Kerry expressed anger and frustration about the Russian cheating and warned that if the violations became widely known, future efforts to convince the Senate to ratify arms control treaties would be harmed.

“If we’re going to have treaties with people, we’ve got to adhere to them,” Kerry said, according to two U.S. officials who read the classified transcript of the hearing. “We’re not going to pass another treaty in the U.S. Senate if our colleagues are sitting up here knowing somebody is cheating.”

Kerry was a major proponent of the New START treaty with Russia, which the Senate ratified after a long debate in December 2010. As secretary of state, he has supported negotiating a follow-on treaty with Russia that could place further limits on the two countries’ stockpiles of strategic and tactical deployed nuclear weapons.

But Kerry knew last year that Russia was in violation of the INF Treaty. That pact, signed by President Reagan, bars development, testing, or deployment of missiles or delivery systems with a range of between 500 and 5,500 kilometers.

“If we’re going to try to reduce more weapons or we’re going to try to have further limits…I can’t look you in the eye, I can’t look anybody in the eye here and say, ‘Hey, vote for this, we haven’t followed through and kept the promises with the prior ones, with the foundations that we’ve built here,” Kerry said inside the hearing.

The exact manner of the Russian cheating remains unclear and highly classified, although there have been several reports that Russia has tested and plans to continue testing two missiles in ways that could violate the terms of the treaty: the SS-25 road mobile intercontinental ballistic missile and the newer RS-26 ICBM, which Russian Deputy Prime Minister Dmitry Rogozin has called “the missile defense killer,” a reference to U.S. plans to expand ballistic missile defense in Europe.

The State Department declined to confirm or deny that it believes Russia is in violation of the treaty and declined to comment on the 2012 briefing with Kerry.

“The administration’s been candid with Congress about a range of countries where we have ongoing treaty compliance issues and are seeking to address them, and that includes concerns we have raised with Russia,” an administration official said. “Determinations about non-compliance are made after a careful process, but Congress is in the loop.”

Some experts say the Obama administration’s failure to acknowledge the treaty violations publicly or confront the Russians about them openly indicates the administration can’t be trusted to take on potential violations by other bad actors with whom it has struck deals, such as the Iranian government and Bashar al-Assad’s regime in Syria.

“If it’s true that the Obama administration has not been candid about—or worse, actively suppressed—information that Russia has violated the Intermediate-Range Nuclear Forces Treaty, then how are congressional lawmakers and the American public supposed to trust that the administration won’t do the same if the Assad regime violates the agreement to remove chemical weapons from Syria or if Iran cheats on the Geneva pact on its nuclear program?” said former congressional staffer Robert Zarate, now policy director of the Foreign Policy Initiative.

Other congressional aides said the Obama administration has briefed certain European allies about the Russian treaty violations but has not informed the entire North Atlantic Council, the political branch of the 27-member North Atlantic Treaty Organization (NATO).

“The INF Treaty is the backbone of protecting Europe from nuclear threats,” said a senior GOP Senate aide. “The fact that the administration will not brief NATO on this issue is a clear indication they place a higher priority on their relationship with Russia than with actual allies in Europe.”

Not all experts agree that the violations are of grave importance. Joe Cirincione, president of the Ploughshares Fund, said treaty violations can be dealt with on a bilateral basis.

“There are real concerns about developments in Russian nuclear strategy,” he said. “But issues of compliance by both nations with arms control treaties are common, and we have reliable methods for resolving these issues. We have to make sure that a compliance problem is not used as an excuse to blow up a threat reduction mechanism that provides real security benefits for the United States.”

But 10 Republican senators disagree and have proposed an amendment to the National Defense Authorization Act (NDAA), obtained by The Daily Beast, that would force the administration to send Congress “a report on information and intelligence sharing with North Atlantic Treaty Organization (NATO) and NATO countries on compliance issues related to the INF Treaty.”

The lead senator on the amendment, Sen. James Risch (R-ID), has been furious about the administration’s handling of Russia’s INF Treaty violations for several months.

Risch confronted Kerry about the cheating at Kerry’s January confirmation hearing, although the senator didn’t say exactly what he was talking about due to the classified nature of the information.

“You and I have sat through some classified briefings, and I don’t want to get into details that we shouldn’t get into, but I’d like your thoughts on where we are at the present time regarding compliance and verification in a general fashion,” Risch said.

Risch also wanted Kerry to promise that any future arms reduction treaties would be sent to the Senate for ratification, considering the past violations, rather than being simply agreed to by the two governments.

“I don’t want to be commenting in some prophylactic way one side or the other without the specific situation in front of me. But I’m confident the president is committed to upholding the Constitution,” Kerry responded, defending the administration’s right to sign agreements without congressional consent.

Risch is one of multiple senators holding up Gottemoeller’s confirmation as undersecretary of state, which has been stalled for months. Sources also said Gottemoeller is being considered to replace Michael McFaul next year as U.S. ambassador to Russia.

Concerns about Russia’s violations of the INF Treaty have been expressed repeatedly by members of the Senate Intelligence Committee and leading House members, including House Armed Services Committee Chairman Buck McKeon and House Permanent Select Committee on Intelligence Chairman Mike Rogers.

“Since October, we have written to you twice with our concerns about a massive Russian violation and circumvention of an arms control obligation to the United States of great significance to this nation and to its NATO allies,” McKeon and Rogers wrote in an April letter to Obama. “Briefings provided by your administration have agreed with your assessment that Russian actions are serious and troubling, but have failed to offer any assurance of any concrete action to address these Russian actions.”

Russian officials have denied they are violating the INF Treaty but at the same time have signaled that at some point the country intends to withdraw from the treaty and pursue development of the currently banned weapons.

Sergei Ivanov, head of the office of President Vladimir Putin, told a Russian TV channel in June that Russia was looking for a way out of the agreement.

“Why is it that everyone and anyone can have this class of weapons and we and the United States cannot?” Ivanov said. “The question arises. On the one hand, we signed the Soviet-American agreement. We perform, but it cannot go o n for infinity.”