Russia’s contract to ferry NASA astronauts to the International Space Station aboard Soyuz rockets will end in April, Deputy Prime Minister Yuri Borisov told reporters on Friday.

The expiration piles additional pressure on the National Aeronautics and Space Administration to restore its capability to shuttle U.S. crew members back and forth to the orbiting lab. The space agency is contracting with Boeing Co. and SpaceX to develop new vehicles to transport astronauts, but the work has been plagued by delays.

NASA has relied on Russia since retirement of the space shuttle in 2011 ended U.S.-controlled access to the space station. Congress and President Donald Trump’s administration have touted the commercial program’s importance to ending that reliance, especially as diplomatic relations between the nations have deteriorated.

A Soyuz flight planned for April 2019 “will complete the fulfillment of our obligations under a contract with NASA related to the delivery of U.S. astronauts to the ISS and their return from the station,” Borisov said at the Energia Rocket and Space Corp., reported by TASS, Russia’s official news agency.

In September 2014, NASA awarded Boeing and Elon Musk’s SpaceX a combined $6.8 billion to revive the U.S.’s ability to fly to the station. SpaceX plans to fly Demo-2, its first test flight with a crew, in April 2019, and Boeing’s Crew Test Flight is now slated for mid-2019, according to a new schedule that NASA released Aug. 2.

Both dates are later than the companies had been targeting. The first Boeing and SpaceX test flights without a crew could occur this year, according to NASA’s most recent flight schedule.

Russia is expected to provide rides for astronauts through November 2019, the planned return date for a Soyuz capsule from the space station, according to a July report to Congress from the Government Accountability Office.

“Obtaining additional Soyuz seats seems unlikely, as the process for manufacturing the spacecraft and contracting for those seats typically takes three years — meaning additional seats would not be available before 2021,” the report said.

Russia charges NASA about $81 million per seat on the Soyuz to fly astronauts to and from the station. NASA signed an agreement in early 2017 to acquire additional Soyuz seats into 2019, although no further contracts involving the Russian craft have been announced.

NASA officials have declined to say whether the agency has discussed procuring additional Soyuz spots with Russian officials.

“As part of its normal operations planning, NASA is continuing to assess multiple scenarios to ensure continued U.S. access to the International Space Station,” NASA spokeswoman Stephanie Schierholz said in an email.