The first crewed flight test of Boeing Co's (BA  ) Starliner spacecraft to the International Space Station will now be launched no earlier than May 17, NASA said on Tuesday, after the launch planned for Monday was halted.

What Happened: The launch planned for Monday was halted after an issue was identified with the Atlas V rocket that was supposed to carry the spacecraft to orbit.

United Launch Alliance, the company operating the rocket, has decided to replace a pressure regulation valve on the liquid oxygen taken on the rocket's Centaur upper stage, NASA said, while adding that the launch is now planned for no earlier than 6:16 p.m. EDT Friday, May 17.

The replacement will begin on Wednesday, May 8, and ULA will also perform leak checks and functional checkouts ahead of the next launch. The two astronauts slated to undertake the flight, Suni Williams and Barry "Butch" Wilmore will remain in quarantine at NASA Kennedy crew quarters in the meantime, the agency said.

Why It Matters: Boeing's Starliner spacecraft has been faced with several delays since the start. The spacecraft was supposed to have its first uncrewed test flight in 2015 which was delayed up to 2019. In 2022, the spacecraft completed its first uncrewed flight to the International Space Station.

If the upcoming crewed flight test is successful, Boeing will become the next private company to shuttle astronauts to and from the ISS for NASA, like Elon Musk's SpaceX.

NASA awarded both Boeing and SpaceX contracts to enable to and from transportation to the ISS after retiring its space shuttle. SpaceX sent its first crewed mission to the ISS in 2020 on its Dragon spacecraft and has since then undertaken multiple missions, overtaking its traditional rival.