Nearly 50 Republican senators warned Iran on Monday that a possible agreement between the U.S. and five other countries on its nuclear agreement might not last long because the next American president may nix the deal, according to Bloomberg. The 47 GOP senators made the warning in an open letter designed to get Iran away from the negotiating table and to let President Barack Obama give Congress more control over the negotiation process.

“It has come to our attention while observing your nuclear negotiations with our government that you may not fully understand our constitutional system,” says the open letter to Iranian leaders. The missive goes on to explain that a deal with Obama that doesn’t include congressional approval “is a mere executive agreement” that can be overturned if the next president doesn’t agree with its terms. The letter also points out that Obama has only two years left in office, while senators have no term limits and some of those who wrote the letter may be in office for “perhaps decades.”

“What these two constitutional provisions mean is that we will consider any agreement regarding your nuclear weapons program that is not approved by the Congress as nothing more than an executive agreement between President Obama and Ayatollah Khamenei,” the letter goes on to say. “The next president could revoke such an executive agreement with the stroke of a pen and future Congresses could modify the terms of the agreement at any time.”

The 47 Republican senators wrote that they hope the letter “enriches your knowledge of our constitutional system and promotes mutual understanding and clarity as nuclear negotiations progress.”

While the letter contains only Republican signatures so far, U.S. Sen. Tom Cotton, R-Ark., who organized the effort, said Democrats are welcome to join their GOP colleagues. “I’d encourage Hillary Clinton to join us,” he said, according to Politico.