TALLINN, Estonia (AP) — Russian authorities on Friday searched the homes of three lawyers representing imprisoned opposition leader Alexei Navalny and detained one of them, the politician’s allies said.

The move against his lawyers is an attempt to “completely isolate Navalny,” his ally Ivan Zhdanov said on social media. Navalny has been behind bars since January 2021, serving a 19-year prison sentence, but has been able to get messages out regularly and keep up with the news.

The raids targeting Vadim Kobzev, Igor Sergunin and Alexei Liptser are part of a criminal case on charges of participating in an extremist group, Zhdanov said. All three were detained after the search, apparently as suspects in the case, Navalny’s team said on Telegram.

According to Leonid Volkov, Navalny’s chief of staff, the case against the lawyers comes at a time when the opposition leader is set to be transferred to a different penal colony, “unclear where.” Volkov, who is living abroad, called it a “scary step.”

For many political prisoners in Russia, regular visits from lawyers — especially in remote regions — are a lifeline that allows them to keep in touch with loved ones and supporters, as well as reporting and pushing back against abuse by prison officials.

Navalny, 47, is President Vladimir Putin’s fiercest foe, campaigning against official corruption and organizing major anti-Kremlin protests. He 2021 arrest came upon his return to Moscow from Germany where he recuperated from nerve agent poisoning that he blamed on the Kremlin. He has since been handed three prison terms, most recently on the charges of extremism.

Navalny’s Anti-Corruption Foundation and a vast network of regional offices were outlawed that same year as extremist groups, a step that exposed anyone involved with them to prosecution.

Navalny has previously rejected all the charges against him as politically motivated and accused the Kremlin of seeking to keep him behind bars for life.

Kobzev was due in court Friday, along with Navalny, for a hearing on two lawsuits the opposition leader had filed against the penal colony where he’s being held. Navalny said at the hearing, which was later adjourned until November, that the case against his lawyers is indicative “of the state of rule of law in Russia.”

“Just like in Soviet times, not only political activists are being prosecuted and turned into political prisoners, but their lawyers, too,” he said.