The source said members of the National Bolshevik Party attempted to break into an office of Surgutneftegas Tuesday morning, demanding back pay for the company's employees.
"Several dozen people attempted to burst into the [Surgutneftegaz] office, shouting slogans and throwing leaflets with demands to pay arrears to the workers," the source said.
He said 27 people were arrested and are facing administrative charges.
"They will probably have to pay fines," he said.
The National Bolsheviks, led by the controversial novelist Eduard Limonov, claim a total of about 15,000 members, most under 18. They are known for their violent protests against government policies and against the Kremlin's alleged violations of democratic principles in the country.
In late September, NBP members burst into the Finance Ministry, throwing leaflets and demanding that bank deposits lost in 1990s be returned to their owners. Witnesses said the trespassers injured a security guard.
A Moscow court banned the organization last June, saying it violated the law on political parties by calling itself a "party" without being officially registered.
The Supreme Court's appeals chamber overturned the ruling in August. But the Prosecutor General challenged the decision with the Supreme Court Presidium, and a panel of Supreme Court justices then ordered a retrial.
In December 2005, 31 NBP activists received suspended sentences, and eight others were sentenced to prison terms ranging from one and a half to three and a half years, for inciting public disturbances when they broke into the presidential staff's visitors' room in December 2004 to protest President Vladimir Putin's political reforms.
The party's leader Limonov was released from prison in 2004 after serving almost two years of a sentence for the illegal possession of small arms.