Eighteen members of the US Congress have moved to block any attempt to readmit Turkey to the F-35 fighter jet program, citing the legal restrictions that remain in force following Ankara’s purchase of the Russian S-400 air defence system.

In a letter addressed to House Majority Leader Steve Scalise and House Minority Leader Hakeem Jeffries, Democratic lawmakers urged congressional leadership to be prepared to exercise the powers granted under US law should the Trump administration seek to proceed with the sale or transfer of American fighter aircraft to Turkey.

The letter was signed by Dina Titus, Chris Pappas, Maggie Goodlander, Grace Meng, Frank Pallone Jr., Brad Schneider, Josh Gottheimer, Jared Moskowitz, Ted Lieu, Brad Sherman, Mike Quigley, Dan Goldman, James McGovern, Stephen Lynch, Jim Costa, George Latimer, Gabe Amo and Robert Menendez.

The initiative, led by Congresswoman Dina Titus, comes ahead of the NATO Summit in Ankara on 7 and 8 July, amid reports that the US administration is exploring ways to reinstate Turkey in the fifth-generation fighter aircraft program.

The lawmakers also point to recent remarks by President Donald Trump, who suggested he intended to offer Turkish President Recep Tayyip Erdogan “a big gift”, as well as comments by Vice President JD Vance indicating that officials are assessing how such a sale could legally proceed.

The letter recalls that the United States removed Turkey from the F-35 program in 2019 after Ankara acquired the Russian-made S-400 missile defence system. Washington concluded that operating the Russian system alongside the US-built fighter aircraft could compromise highly sensitive information about the F-35’s capabilities.

The lawmakers also note that, in December 2020, the Trump administration imposed sanctions on Turkey’s Presidency of Defence Industries under the Countering America’s Adversaries Through Sanctions Act (CAATSA) in response to the S-400 purchase. They stress that those sanctions have never been lifted and remain legally in force.

From a legal standpoint, the signatories cite both CAATSA and the National Defense Authorization Act for Fiscal Year 2020, which prohibits the transfer of F-35 aircraft to Turkey as long as Ankara continues to possess the S-400 system and has not provided the required assurances that it will not seek to acquire the system again.

According to the letter, there is no publicly available evidence that Turkey has removed the Russian air defence system, taken it out of operational service, or otherwise eliminated the circumstances that led to the sanctions being imposed.

The lawmakers argue that, under these conditions, any attempt to readmit Turkey to the F-35 program would place the US administration in breach of its legal obligations.

They also refer to testimony given by Secretary of State Marco Rubio before the House Foreign Affairs Committee on 3 June 2026. According to the letter, Rubio acknowledged that the administration is legally required to maintain sanctions against Turkey and cannot reinstate Ankara in the F-35 program under the current circumstances.

Beyond the legal issues, the signatories warn that such a move would send the wrong strategic message to US partners in the Eastern Mediterranean. They cite Turkey’s policy towards Greece and Cyprus, its support for Azerbaijan during its military operations against Armenia, and Ankara’s stance towards Israel.

According to the lawmakers, supplying Turkey with one of the United States’ most advanced weapons systems without addressing the reasons behind its removal from the program could encourage further destabilising behaviour and undermine the confidence of allies that have complied with the established rules.

The lawmakers further emphasise that CAATSA was passed with overwhelming bipartisan support to ensure that Congress retains meaningful oversight of decisions involving the transfer of advanced US military technology to countries that have engaged in significant defence transactions with America’s adversaries.

“The integrity of this framework, and the message it sends to any country considering the purchase of Russian weapons, depends on Congress’s willingness to enforce it,” the letter states.