The US has opened up to selling the fighter jets to Turkey but first such a deal must be approved by Congress.
The letter from the senators states that Congress should not consider future aid to Turkey, including an F-16 deal, until Sweden and Finland are admitted to NATO.
“Failure to ratify the protocol or provide a timetable for ratification threatens alliance unity at a crucial moment in history as Russia continues its unprovoked invasion of Ukraine,” the letter said.
Senators from both Democrats and Republicans have signed the letter, including former Democratic presidential hopefuls Amy Klobuchar and Kirsten Gillibrand as well as Alaska Republican Lisa Murkowski.