At least 50 journalists from a Russian publisher have signed an open letter complaining they are being prevented from publishing critical statements about Prime Minister Vladimir Putin after two of their colleagues were fired.

An editor and senior manager of Kommersant Publishing were fired on Tuesday in connection with what the owner, Alisher Usmanov, has described as a breach of ethics for its coverage of the parliamentary elections in the Kommersant Vlast weekly magazine. The article alleged fraud alongside images of Mr. Putin containing expletives.

In an open letter posted on the internet Wednesday, reporters for the publisher argued that the firing is an “act of intimidation aimed at preventing any critical statements about Vladimir Putin.”

Usmanov has defended his decision, adding that he has no intention of selling the publication despite an early buy-out offer from fellow tycoon Mikhail Prokhorov, who launched a bid this week to challenge Mr. Putin for the presidency.

The December 4 parliamentary elections saw United Russia lose support with a reduced majority in the State Duma. Reports of widespread fraud led to anti-government demonstrations across the country.

Leaders of United Russia — which has dominated Russian politics for more than a decade — have denied cheating.

If Mr. Putin regains the presidency, the 59-year-old leader could serve two more six-year terms and remain in power until 2024. He was first elected president in 2000 and held that post until 2008, when he assumed the post of prime minister due to term limits.

Wednesday, a leading ally of Russian Prime Minister Vladimir Putin resigned as speaker of the country's parliament. Boris Gryzlov was elected as speaker in 2003. He said he would renounce his mandate as a member of parliament, but will continue his post as chairman of United Russia.