NASA is suspending its work with Russia except for the International Space Station.
The move comes a week after the space agency said U.S.-Russian space relations were fine despite Russia's annexation of the Crimean Peninsula from Ukraine.
NASA employees are barred from travelling to Russia until further notice. Workers also can't email or hold teleconferences with their Russian counterparts.
The space station is unaffected. A Russian rocket recently delivered three astronauts, including an American, to the orbiting outpost.
Space policy experts said they're not surprised because similar memos went out to other federal agencies. They think the impact is limited since the countries will continue to co-operate on the space station.