President Biden should make clear to Turkish President Recep Tayyip Erdoğan that Congress is unlikely to approve fighter jet upgrades for Ankara if it fails to advance Sweden and Finland’s bid to join NATO, a bipartisan group of senators said Thursday.

Sens. Jeanne Shaheen (DN.H.) and Thom Tillis (RN.C.), co-chairs of the Senate NATO Observer Group, led 25 of their colleagues in a letter to the presidentand said: “Congress cannot consider future support for Türkiye, including the sale of F-16 fighter jets, until Türkiye completes ratification of the Accession Protocols.”

Of NATO’s 30 members, only Turkey and Hungary have not yet ratified the accession of Sweden and Finland. Budapest is expected to adopt the protocols this month.

“Failure to ratify the protocols or present a timeline for ratification threatens the alliance’s unity at a key moment in history, as Russia continues its unprovoked invasion of Ukraine,” the senators wrote.

They further supported Finland’s and Sweden’s commitments to address Turkey’s security concerns originally raised when Helsinki and Stockholm first announced their intention to join the alliance, but criticized Ankara for going back on those commitments.

The administration is unlikely to move forward with plans to provide Turkey with modernization kits for its F-16s and allow Ankara to buy more fighter jets, as Senate Foreign Relations Committee Chairman Robert Menendez (DN.J.), who did not sign the bipartisan letter, has said he would oppose any such sales.

A senior US official told Reuters that it was “doubtful” that the administration would be able to move forward unless Menendez dropped his objection.

Biden administration officials have indicated to Turkey that Congress opposes security improvements to its fleet of F-16s and potential sales of new ones if Ankara fails to ratify Sweden’s and Finland’s bid to join NATO, Secretary of State for Political Affairs Victoria Nuland said during a foreign affairs hearing in the Senate last week.

“We’ve made the same point to our Turkish allies… that we need this Congress’s support, to move forward on the security enhancements that we think they need, as allies, the F16s, some of them are old, but that this Congress is likely to to look at it much more positively after ratification,” Nuland said, urging the senators to “continue to make your points and we will as well.”

Erdoğan has said in recent days that he opposes Sweden’s bid to join NATO amid tensions between Ankara and Stockholm, most notably criticizing Stockholm for failing to impose costs after a Danish far-right politician burned a copy of the Koran during a protest. Stockholm says that the measure falls within the right to freedom of expression.

Turkey, Finland and Sweden signed a memorandum of understanding in June to address Ankara’s concerns over a number of issues, but in particular how Sweden, and to some extent Finland, treats the Kurdistan Workers’ Party, or PKK, which Turkey, the European Union and the United States consider a terrorist organization.

Erdoğan has said that Turkey looks positive on Finland’s ascension but not Sweden’s.

“Our position on Finland is positive, but it is not positive for Sweden,” he said in a speech to his AK Party deputies in parliament, Reuters reported.

In a joint statement, the Presidential and Cabinet Committee on Finland’s Security and Foreign Policy said that Finland plans to advance its membership process together with Sweden, Reuters reported.

“That the fastest possible realization of both countries’ membership is in the interest of Finland, Sweden and the whole of NATO,” the statement read.