Space, mankind's biggest hurdle; a place where Earthly concerns are cast aside as humanity bravely straddles a new age - until an argument breaks out over the toilet.

Once a haven of international understanding where resources and food were openly shared, it seems not even the International Space Station is immune to the forces of commercialism.

Now a Russian cosmonaut has been told he can no longer use a US toilet or exercise bike.

Gennady Padalka, 50, told Russia's Novaya Gazeta newspaper the problem was due to the ISS becoming a more commercial operation.

The cosmonaut said the lack of sharing was lowering the crew's morale and marks a shift since his first mission in 1998, where crews from different nations worked in harmony.

This began to change when Moscow started billing the US for sending astronauts into space, Padalka said.

"What is going on has an adverse effect on our work," Padalka told the newspaper.

Padalka had asked if he could US facilities on the ISS to stay fit before he blasted off on Thrusday.

"They told me: 'Yes, you can.' Then they said no," Padalka is quoted as saying.

"Then they hold consultations and they approve it again. And now, right before the flight, it turns out again that the answer is negative."

Padalka says regulations require US and Russian cosmonauts now only eat their own rations.

"They also recommend us to only use national toilets," Padalka told the newspaper.

"Cosmonauts are above the ongoing squabble, no matter what officials decide," he told the Novaya Gazeta. "It's politicians and bureaucrats who can't reach agreement, not us."