Iran’s Supreme Leader Ayatollah Khamenei said Wednesday the United States’ potential extension of sanctions under a 20-year-old law could violate a landmark nuclear agreement between the two nations. He threatened stern reaction in response to an overwhelming vote by the House of Representatives last week to extend sanctions on Iran, Reuters reported Wednesday. 

Speaking to members of the Revolutionary Guard, Khamenei accused the U.S. of repeatedly breaking the deal struck in Vienna in July 2015 that would roll back Iran’s nuclear program in exchange for decreased economic sanctions.

"The current U.S. government has breached the nuclear deal in many occasions," Khamenei said. "The latest is extension of sanctions for 10 years, that if it happens, would surely be against JCPOA, and the Islamic Republic would definitely react to it."

JCPOA, or the Joint Comprehensive Plan of Action, is a joint effort by the U.S., Iran, Britain, France, Germany, Russia and China over the best way to prevent Tehran from developing nuclear weapons. It calls for Iran to limit nuclear production for 10 years and comply with the International Atomic Energy Agency. The plan was opposed by Saudi Arabia and Israel.

Khamenei was directly responding to the House’s vote last week to extend sanctions on Iran for 10 years under the Iran Sanctions Act of 1996. The House reached an overwhelming 419 to 1 conclusion, but the extension must still pass the Senate and get approval from President Barack Obama. Obama’s administration has said he will veto the bill if it reaches his desk.

Khamenei wasn’t explicit about what Iran’s reaction might be, or what it could even do. He didn’t name any other specific U.S. “violation.” However, his comments could re-ignite tensions between the two nations that the historic nuclear pact somewhat assuaged. The lifting of the sanctions has also proven beneficial to Iran’s economy, allowing it’s oil production to soar of late.

Going forward, much of the tension over the nuclear deal will fall at the feet of President-elect Donald Trump, who often trashed it on the campaign trail.