Russia's space agency voiced outrage Tuesday after the defence ministry refused one of its cosmonauts a celebrated state honour, in the first such snub in half a century of Soyuz flights.

Cosmonaut Maxim Surayev, who returned to Earth in March after six months aboard the International Space Station (ISS), has twice been denied the Hero of Russia medal, in what the media has called a "scandal of cosmic proportions."

"The defence ministry has twice refused to award the Hero of Russia medal to Surayev," Roskosmos spokesman Alexander Vorobyov told AFP. "As far as I know there was no reason given."

The accolade -- one of the country's highest honours -- has been granted to nearly every first-time cosmonaut since pioneer spaceman Yuri Gagarin in 1961 and to every Russian to fly on the Soyuz craft since the breakup of the Soviet Union.

"The entire Russian cosmonaut community is up in arms at what is happening and in the end they may all go on strike," Vorobyov said, adding that the space agency had appealed to President Dmitry Medvedev to intervene.

The Hero of Russia medal confers housing, pension and travel benefits, as well as a state funeral.

These perks compensate cosmonauts for wages much lower than those paid to astronauts in the United States space programme NASA, Vorobyov argued.

"Our cosmonauts earn a lot less than NASA's astronauts, so in some ways it is a moral compensation," he said. "If they're not going to make them Heroes, then at the least they have to raise their salaries."

First-time cosmonaut Surayev, 38, became the first Russian to write a blog about his time in orbit with witty entries full of sharp Cold War spoofs and also went on a tricky spacewalk.

Cosmonaut colleagues argued he had done enough to deserve the honour.

"They probably thought that we don't do anything there (in space)... just fly up there for a vacation," Roman Romanenko, 39, who was awarded the honour in May, said on Russian television last week.

"I think it's wrong and I'm not the only one who thinks so."

Veteran Soviet cosmonaut Magomed Tolboyev, 59, also expressed indignation over what he saw as an arbitrary bureaucrat's decision.

"Make that bureaucrat sit in a space ship and launch it!" Tolboyev raged in comments posted on Roskosmos' website.

"Let him then judge what cosmonauts do: They're real men!"

But the rejection has also ignited controversy over whether cosmonauts are in fact worthy of the semi-automatic bestowal of rank -- now that the risks have become almost everyday, even attracting a generation of space tourists.

"Are cosmonauts no longer heroes?" the daily Nezavisimaya Gazeta queried in an editorial Tuesday that compared today's almost routine space flights with the pioneering ones of the 1960s, when cosmonauts doubted their safe return.

By contrast, similar awards have been rarely handed down to US astronauts by Russia's erstwhile Cold War challenger NASA, the paper noted.

Since the first US space flight, only 28 honorary medals have been awarded to a handful of NASA's 400 space-tried astronauts.

"It looks as if what is for foreigners everyday work and fun, for Russians is a heroic exploit," the paper wrote.

Pavel Vinogradov, who won honors for numerous spacewalks to repair the Soviet-era Mir station, broke rank with colleagues, saying it was high time they stopped taking perks for granted.

"The time has ended for automatically pinning gold stars to the chests of everyone going to space," Vinogradov was quoted by the paper as saying.