Guinean media called a 24-hour strike for Thursday in protest at the government's closure of an opposition-owned radio station for one month before the June 30 election after a listener called on the air for an uprising.
The long-delayed vote is supposed to seal a democratic transition after a 2008 military coup in the mineral-rich West African nation. But the opposition says it fears the ballot will be rigged and has staged violent protests to try to block it.
Increasing political tension has alarmed many investors in the West African country, the world's largest exporter of bauxite, threatening to deter much-needed capital as it seeks to diversify its economy.
The state communications regulator suspended Planete FM radio on Thursday after a caller urged a revolt against President Alpha Conde. Planete FM, owned by opposition spokesman Abdoulaye Sylla, cut the caller off and criticized his appeal.
"The National Communications Council's decision respects neither the law on freedom of the press nor the constitution," said Boubacar Yacine Diallo, head of the URTELGUI media association. "We demand that the CNC revoke this sanction."
Guinean law allows the closure of private media for a maximum of 72 hours for any act that might threaten state security.
International media watchdog Reporters Without Borders said in a statement the CNC was acting like an institution "outside the law" as its ruling was based on a 1991 statute which had been superseded by subsequent legislation.
More than 50 people have died in three months of political violence and ethnic clashes between pro-opposition Peuls and the Malinke group which supports the government.
Guinean media have reported an increasing number of violent attacks on journalists by both government and opposition supporters. "Journalists have been attacked and threatened, radio stations have been attacked, all during political protests," Diallo said.
Conde has ordered an investigation into a round of protests in late May in which 12 people died in clashes between police and demonstrators.
The opposition has called on the government to revoke the licence of South Africa's Waymark to update the voter list, saying Waymark is stuffing the register with Malinke voters.
The company denies this and the government says there is no time to appoint a new company to do the job.