The husband of a prominent opposition leader was convicted a second time on fraud charges Thursday and sentenced to five years in a labor camp. Activists interpreted the sentence as a warning to protesters who have been demonstrating against Vladimir Putin.

Alexei Kozlov, the husband of activist journalist Olga Romanova, was first arrested in 2008 on fraud charges related to a business involving a well-connected partner. Such cases are considered common here, with businessmen often charged with crimes as part of efforts to steal their businesses or extract bribes. Though Kozlov was convicted and sentenced to eight years in prison, Romanova managed to drive the case to the Supreme Court, which ordered his release in September after he had served three years in Siberia.

At a court hearing Sunday, prosecutors renewed the case, leading to Thursday’s re-conviction.

Romanova became politically active after her court battles, taking on a leading role in organizing recent demonstrations. After Kozlov’s sentence Thursday, she told reporters Russia would never achieve freedom or fair elections without judicial reform.

Lyudmila Alekseyeva, the head of the Moscow Helsinki Group, told the Interfax news agency, “I believe it’s retaliation against him and especially his wife for their rally activities.”

Also Thursday, Sergei Udaltsov, leader of the socialist Left Front, was sentenced to 10 days in jail for leading a procession of followers toward a nearby square after a rally for fair elections Saturday. Influential blogger Alexei Navalny was fined the equivalent of $34 for failing to leave a March 5 anti-Putin demonstration promptly.

And a third member of a feminist punk band was detained after being called as a witness against the two others, who are already in jail facing seven-year sentences for singing an anti-Putin song on the altar of Moscow’s Cathedral of Christ the Savior.

After his court appearance, Navalny tweeted about the Kozlov case, “It’s retaliation against Romanova.”