NASA is to launch a review of Elon Musk's SpaceX after the entrepreneur smoked marijuana on a podcast.
The US space agency, which has a contract with the company to fly its astronauts, said it would run a "cultural assessment study" into its commercial partners to make sure they are following its no-drug policies.
SpaceX, which Mr Musk runs alongside Tesla, is one of the private companies developing spacecraft designed to fly astronauts to the International Space Station.
Its first launch piloted by NASA astronauts on the spacecraft Crew Dragon is due to take place in June next year. Its first test with no crew is set for January.
NASA also has a contract with Boeing, whose spacecraft Starliner is set to launch without crew in March and with astronauts on board in August.
"In the coming months, prior to the crew test flights of Crew Dragon and Starliner, NASA will be conducting a cultural assessment study in coordination with our commercial partners to ensure the companies are meeting NASA’s requirements for workplace safety, including the adherence to a drug-free environment," the agency said.
"We fully expect our commercial partners to meet all workplace safety requirements in the execution of our missions and the services they provide the American people."
Mr Musk prompted controversy in September after he smoked the drug, which is legal in California, on the podcast the Joe Rogan Experience.
He is the founder, chief executive and lead designer at the space company, which he runs alongside electric car company Tesla.
The NASA review is thought to have been prompted by concerns at NASA about his drug use.
In an interview, NASA Administrator Jim Bridenstine told the Washington Post: "If I see something that’s inappropriate, the key concern to me is what is the culture that led to that inappropriateness and is NASA involved in that."
He added that "culture and leadership start at the top. Anything that would result in some questioning the culture of safety, we need to fix immediately."
A spokesman for SpaceX said the company "actively promotes workplace safety, and we are confident that our comprehensive drug-free workforce and workplace programs exceed all applicable contractual requirements."