The Venezuelan government has cancelled the passports of dozens of journalists and activists since President Nicolás Maduro claimed a re-election victory, part of what rights groups said is an intensifying campaign of repression against the authoritarian president’s opponents, the Financial Times has reported.

At least 40 people, mostly journalists and human rights activists, have had their passports annulled without explanation, the newspaper reported on Saturday, citing Caracas-based rights group Laboratorio de Paz.

The group warned that the number of people who have had their passports cancelled is likely to be much higher due to Venezuelans’ fear of reporting cases, the FT said.

Laboratorio de Paz could not be immediately reached about the report.

People have had their passports confiscated by authorities while attempting to board flights from the country’s main airport, the newspaper said, citing the rights group.

Unlike murder or torture, which have a higher political cost, the government has found that passport cancellation is an effective way of neutralising and muffling critical voices with minimal effort, the newspaper reported, citing Rafael Uzcátegui, co-director of the rights group.

Maduro was proclaimed the winner of the South American nation’s disputed July vote by electoral and judicial authorities, a claim rejected as false by the opposition.