The Russian space agency Roscosmos has said it will not launch satellites part-owned by the British government without guarantees they will not be used for military purposes.
A Soyuz rocket carrying 36 satellites for the internet firm OneWeb is due to go up from the Baikonur Cosmodrome in Kazakhstan on Friday.
Roscosmos head Dmitry Rogozin said OneWeb had two days to provide “legally binding” guarantees.
OneWeb has yet to comment.
But the UK government is coming under pressure to pull the launch over the Russian invasion of Ukraine.
UK taxpayers helped buy OneWeb out of bankruptcy in 2020 with a £400m stake.
In an interview with Russia 24 TV channel, Mr Rogozin said Roscomos had contacted OneWeb and its partner Arianespace to demand “comprehensive legally binding guarantees” that the satellites would not be used for military purposes.
“If by 21:30 on March 4 we do not receive confirmation, the rocket will be removed from the launch pad and the satellites will be sent to the assembly and test building,” he added.
The launch is currently timed for 22:41 GMT on Friday (03:41 local, Saturday).
According to Russian news agency TASS, Mr Rogozin said the OneWeb contract had been paid in full and the funds would not be returned.
“We received all the money for it for the manufacture of launch vehicles, upper-stages and for the necessary launch services.
“This money, due to force majeure circumstances that have arisen as a result of the aggressive policy of the West and the sanctions that are applied against Russia, this money will remain in Russia,” added the Roscosmos boss.
OneWeb has just a handful of launches left to complete its network of 648 satellites.
All of the missions are booked on Russian Soyuz vehicles that are scheduled to fly out of Baikonur in the coming months.
With the existing spacecraft it has in orbit (428), the company can deliver broadband internet connections to locations above 50 degrees North, which includes business customers such as BT in the UK, but it needs those additional satellites if it wants to run a truly global service.
Regions important to the company’s prospects, including the rest of Europe, Africa and Asia, would be left out.
A UK government spokesperson told BBC News: “It is right for questions to be raised about future space cooperation with Russia following the illegal invasion of Ukraine. We are monitoring the situation closely and engaging regularly with our partners, keeping next steps under review.”
