A lawyer for jailed Russian oil tycoon Mikhail Khodorkovsky on Friday appealed his sentence of six more years in prison, a punishment seen as payback for challenging Vladimir Putin’s power and which was widely condemned in the West.

Khodorkovsky’s lawyer Karinna Moskalenko told The Associated Press she launched the appeal on the final work day before a 10-day New Year vacation. She said Khodorkovsky’s conviction on charges of stealing almost $30 billion worth of oil from his company and laundering the proceeds was marred by procedural violations.