Police in Moscow have detained Sergey Boyko, the coordinator of Alexey Navalny’s headquarters in Novosibirsk, on charges of repeatedly violating Russia’s laws on public demonstrations.

According to Vyacheslav Gimadi, a lawyer for the Anti-Corruption Foundation, the evidence against Boyko is a tweet he posted on April 12, where he called on people to protest against Vladimir Putin on May 5. The tweet, which includes a link to Alexey Navalny’s website, doesn’t mention a time or a location, and it was too early to know if Moscow city officials would grant a demonstration permit (they didn’t).

On May 5, Alexey Navalny and his supporters organized nationwide protests against Vladimir Putin’s fourth inauguration. Police officers arrested more than 1,600 demonstrators in cities across the country. Navalny was detained and later sentenced to 30 days in jail.