Since its inception, NASA’s Commercial Crew Program has been hampered by setback after setback, and it looks like even more delays are on the horizon for the fledgling initiative. The program — which tasks US private companies with building spacecraft that can transport NASA astronauts to and from the International Space Station — was originally supposed to get off the ground in 2017. But SpaceX and Boeing, the two companies that are developing these crewed spacecraft for NASA, probably won’t have their vehicles certified to carry astronauts until 2019.

That’s according to a new report from the Government Accountability Office, a federal agency that does audits for Congress. The report highlights a number of problems that threaten to push back the first crewed flights for the Commercial Crew Program, such as design challenges and risks that need to be addressed by both SpaceX and Boeing. Because of the likelihood for delays, the GAO report recommends that NASA come up with a backup plan for getting its astronauts to the ISS beyond 2018.

Currently, NASA astronauts only have one way to get to the station: on Russia’s Soyuz rocket. The space agency has to buy seats on the Soyuz for its astronauts — tickets that cost about $80 million per person. But once the Commercial Crew Program gets up and running, NASA astronauts will be able to launch on American made vehicles again, for a relatively cheaper cost. For the program, Boeing is developing a crew capsule called the CST-100 Starliner, which is meant to launch on top of the Atlas V rocket manufactured by the United Launch Alliance. Meanwhile, SpaceX is upgrading its Dragon cargo capsule, which is already used to ship supplies to the station, so that it can carry humans to space. This Crew Dragon is meant to fly on top of SpaceX’s Falcon 9 rocket.

However, SpaceX and Boeing won’t be able to start flying astronauts regularly to the ISS until their vehicles have been certified by NASA. For that to happen, each company has to conduct a crewed test flight, carrying astronauts to the station like they would for a regular mission. SpaceX and Boeing are both targeting 2018 for those test flights, but the GAO report identifies a number of reasons why the vehicles won’t be certified until the year after.

For SpaceX, the problems seem to revolve around design changes that need to be addressed by the company. A report surfaced a week ago that a pattern of cracking had been found in the turbines of SpaceX’s engines, which NASA said was an “unacceptable risk.” SpaceX says it is working to eliminate the defect before crewed flights take place. Additionally, the company is in the middle of upgrading its Falcon 9 to a new version of the vehicle called the Block 5. The upgrade includes five major changes to the rocket’s design, and the GAO report claims that there may not be enough time for these changes to be implemented and reviewed by NASA before SpaceX’s first uncrewed flight test of the Crew Dragon in late 2017.

As for Boeing, the company seems to be having trouble gathering important information that NASA needs to certify the CST-100 Starliner. For instance, the Atlas V rocket that is supposed to carry the Starliner into space uses Russian-made rocket engines. But because of agreements between the US and Russia, getting information related to the design of the engine has been difficult, making it hard for NASA to okay the engines for human spaceflight. Additionally, there are concerns if Boeing will be able to get enough data about how the Starliner’s parachutes work before humans fly in the vehicle for the first time.

Both Boeing and SpaceX have already been forced to delay the first crewed test flights of their vehicles to August and May 2018, respectively. NASA has already prepared for this setback by purchasing additional Soyuz seats for its astronauts through 2018. But the GAO report suggests that NASA should think about potentially buying even more Soyuz seats for 2019, especially since it takes about three years to process those requests. The space agency has already expressed interest in purchasing three additional Soyuz seats for early 2019, but if the Commercial Crew Program continues to be delayed, NASA may experience a gap in access to the station in a couple of years.

“Without a viable contingency option for ensuring uninterrupted access to the ISS in the event of further Commercial Crew delays, NASA risks not being able to maximize the return on its multibillion dollar investment in the space station,” the GAO report states.

NASA says it agrees with the GAO report’s recommendations and plans to come up with a contingency plan by March 13th.