Turkey is taking possession of two F-35 aircraft this week, but US lawmakers may yet deny Ankara critical American technology needed to get the warplanes off the ground.

There appears to be little Congress can do to stop Turkey from obtaining the two jets, the first of more than 100, as Lockheed Martin prepares to hand them over to Turkish pilots at a ceremony in Texas on Thursday. But US lawmakers still have considerable leverage as they consider pending defense legislation that seeks to hold up the sale amid concerns about Turkey’s planned purchase of the S-400 missile-defense system from Russia and its imprisonment of a US pastor.

A US Defense Department official told Al-Monitor that Turkey won’t be able to take the jets home for a considerable period of time, requiring American support to run the F-35’s computerized logistics system and navigate security protocols. That in turn could give lawmakers leverage to deny the use of crucial technology needed for Turkey to operate the aircraft if relations with the NATO ally continue to deteriorate.

Language in the pending Senate bill would deny the transfer of title to Turkey until the Pentagon proposes a plan to remove Turkey from the F-35 construction program, a joint effort between seven nations. Turkey is contributing technology to the jet, including work on the plane’s central fuselage.