The Biden administration is set to notify Congress in the coming days of the potential sale of F-16 fighter jets to Turkey, sources familiar with the matter said on Friday.

The U.S. State Department is likely to kick off an informal notification process called a “tiered review” next week, sources said, a bureaucratic step in notifying Congress of major arms sales.

NATO member Turkey requested in October 2021 to buy 40 Lockheed Martin Corp (LMT.N) F-16 fighters and nearly 80 modernization kits for its existing warplanes. Technical talks between the two sides recently concluded.

The notification would come as Turkish foreign minister Mevlut Cavusoglu prepares to visit Washington on Jan. 18 for bilateral talks amid a host of problems between the two NATO allies ranging from disagreement over Syria policy to Ankara’s purchase of Russian weapons.

“As a matter of policy, we do not confirm or comment on proposed defense sales or transfers until they have been formally notified to Congress,” a State Department spokesperson said.

The Biden administration has said it supports the sale and has been in touch with Congress on an informal basis to ensure that lawmakers would not block it.

However, it is yet to secure a green light from the Congress. While the F-16 purchase has critics and supporters in both parties, Bob Menendez, Democratic chair of the Senate Foreign Relations Committee, has repeatedly said he opposes the sale, citing Turkey’s human rights track record and planned incursion into Syria.

Turkey’s purchase of the Russian S-400 air defense systems has resulted in Ankara being kicked out of the next generation F-35 fighter jet program and antagonized the U.S. Congress.

Analysts have said it would be unlikely for the U.S. Congress to give the green light for the sale unless Ankara ratifies the NATO membership for Sweden and Finland.

The two countries applied in May to join NATO in response to Russia’s invasion of Ukraine, but Turkey objected and accused the countries of harboring militants, including from the outlawed Kurdistan Workers’ Party.