A bipartisan group of House members urged the administration to “be very careful” in negotiations with Turkey about its potential re-entry into a program allowing it to acquire and potentially co-produce F-35 fighter jets, ahead of a White House meeting between President Donald Trump and Turkish President Recep Tayyip Erdogan on Thursday.

Trump said Friday that he would host Erdogan at the White House for trade and military talks, “including the large-scale purchase of Boeing aircraft, a major F-16 Deal, and a continuation of the F-35 talks, which we expect to conclude positively.” 

Lawmakers have been pressing for months for the administration to be cautious in allowing Turkey to acquire the advanced fighter jets, something it has been banned by law from doing since it purchased a Russian S-400 missile defense system. By law, Turkey must dispense with that system before it can be re-admitted into the F-35 program, but some lawmakers have pushed for additional conditions, given various conflicts with Turkey, including its hostile posture toward Israel.

“The United States must be very careful when engaging in negotiations particularly as it relates to discussions surrounding Turkey’s potential reentry into the F-35 Joint Strike Fighter program. Turkey was rightfully removed from the program in 2019 following its acquisition of the Russian-made S-400 missile defense system—a clear violation of U.S. law under the Countering America’s Adversaries Through Sanctions Act (CAATSA),” Reps. Gus Bilirakis (R-FL), Chris Pappas (D-NH), Nicole Malliotakis (R-NY) and Dina Titus (D-NV), who chair the Congressional Hellenic Caucus, said in a joint statement on Monday.

They emphasized that the Turkish-Russian cooperation, in spite of Turkey’s NATO status, “directly undermines the security of U.S. defense technology and poses a threat to the strategic integrity of allied defense cooperation,” as well as “risks exposing sensitive U.S. military capabilities to Russian intelligence, eroding allied trust, and jeopardizing the development of next-generation military platforms.”

In addition to the formal legal obstacles that should ban F-35 acquisition under current conditions, the four lawmakers added that Erdogan has “consistently demonstrated a disregard for international norms and democratic principles.”

They said that upholding the sanctions law is critical both to protect U.S. defense technology as well as to demonstrate the U.S.’s commitment to the rule of law.

“Rewarding Erdogan’s government without meaningful changes in behavior would set a dangerous precedent and weaken the credibility of U.S. foreign policy,” the lawmakers wrote. “The United States must stand firm in defending its laws, its alliances, and the international order.”