A Kremlin spokesman suggested Tuesday that a call by Russian opposition leader Alexi Navalny to boycott next year’s presidential election may be illegal.

Navalny urged supporters to boycott the March 18 vote after election officials on Monday barred him from running.

Russia’s Central Election Commission (CEC) voted to ban the anti-corruption blogger from running because of his conviction on criminal charges. Navalny and his followers say those charges were politically motivated.

Following the CEC decision, Navalny released a video declaring a “voter’s strike,” because — according to Navalny — the March contest would not really be an election.

Dmitry Peskov, a spokesman for Russian President Vladimir Putin, said Tuesday that efforts by Navalny and his supporters to organize the boycott “ought to be carefully studied to see if they are breaking the law.”

Putin announced earlier this month that he will run for reelection, and it is widely assumed he will win a fourth term as Russian head of state.