The move comes amid a diplomatic standoff between Turkiye and Sweden over what the former claims is Swedish support for terror groups and sympathizers.

Both Sweden and Finland announced their NATO bid last year following the Russian invasion of Ukraine.

However, Ankara has set preconditions in exchange for Turkish ratification of the membership applications, asking both Nordic countries to toughen their stance against the outlawed Kurdistan Workers’ Party (PKK), deport certain individuals, and review their regulatory framework for arms exports.

Turkish President Recep Tayyip Erdogan accused both countries of being “guesthouses for terror organizations.”

After a far-right Danish politician recently burned a copy of the Qur’an near the Turkish Embassy in Stockholm, Turkiye suspended trilateral talks with Sweden and Finland, and postponed a meeting between Turkish and Swedish defense ministers in Ankara.

Although Ankara hinted at the possibility it would approve Finnish NATO accession before Sweden’s, Helsinki rejected the offer, saying that the security of both countries is dependent on each other.

In their letter to Biden, the US senators said that the two Nordic countries were “making full and good faith efforts to meet the conditions for NATO membership that Turkiye asked.”

The senators said that they could not promise any automatic sale of F-16s if Ankara agreed to the Finnish and Swedish request, but warned they “won’t even ponder this sale” in the absence of ratification.

“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 letter said.

For the first time, members of Congress are insisting on linking the sale of F-16 fighter jets to Turkiye with the ratification of the NATO accession bids by the two Nordic countries.

In January, CNN quoted Congressional sources saying that the Biden administration is preparing to ask lawmakers to approve the F-16s sale.

If approved, it will be one of the largest US arms sales in recent years.

Turkiye has been waiting for the sale of 40 F-16 fighters and almost 80 modernization kits for its existing fleet since October 2021.

Last month, Turkish Foreign Minister Mevlut Cavusoglu visited Washington and said that the Nordic NATO accession should not be tied with the F-16 sale.

Rich Outzen, senior fellow at Atlantic Council, sees little chance of some US senators, such as Robert Menendez, the Democrat chair of the Senate Foreign Relations Committee, and Senate Foreign Relations Committee member Chris Van Hollen, changing their position on the F-16s even if Ankara green lights the Swedish request while Erdogan remains in office.

“They have a winning domestic political issue with a range of constituencies that dislike Turkiye, including the Greek lobby, Armenian lobby, and Syrian Kurdish YPG-sympathetic activists. With such rewards, there is little incentive to cede ground,” he told Arab News.

New Jersey, Menendez’s home state, has a large Greek-American and Armenian-American community.

In a message posted on Twitter in December, Menendez said he that would not “approve F-16s for Turkiye until Erdogan halts his abuses across the region,” referring to longstanding tensions between Turkiye and Greece over airspace, and the militarization of islands in the Aegean.

Arms sales to foreign countries are subject to congressional approval. But Congress alone cannot block foreign arms sales.

However, experts say that Ankara’s ratification of the NATO accession of Sweden and Finland would facilitate the sale process in Congress.

According to Outzen, “transactional politics” on defense deals can work when done privately and reciprocally, but the F-16 deal has become a public issue with conflicting demands.

“It makes near-term resolution almost impossible,” he said.

Sinan Ulgen, a former Turkish diplomat and chairman of the Istanbul-based think tank EDAM, said that the senators’ letter is not surprising since NATO enlargement is a priority for the alliance and the US.

He added that “it is not at all guaranteed” that the F-16 sale will be approved, even if Ankara ratifies the Finnish and Swedish request.

Ulgen believes the White House may have to rely on the presidential prerogative to override Congressional opposition.

“But (Biden) will be much less willing to use this political prerogative, unlike his predecessor Donald Trump, who did not have a long political experience with the Congress,” he said.

Turkiye was expelled by the US from its fifth-generation F-35 joint strike fighter program in 2019 after its purchase of the Russian S-400 missile defense system.

Ankara has requested the F-16 jets instead of reimbursement for the undelivered F-35 fighters, and has said that it will consider alternatives, including from Russia, if the F-16s are not delivered.