Most Tunisians will vote on May 6 in the municipal polls -- the first since the North African country's 2011 revolution -- but members of the security forces cast their ballots a week earlier.

"This is a historic day. For the first time we are exercising a right of citizenship," a police officer told AFP at a polling station in central Tunis, asking to remain anonymous.

Under the long rule of ex-president Zine El Abidine Ben Ali, authorities outlawed voting by soldiers and police, insisting security forces remain outside of politics.

But after Ben Ali's fall, long-banned police unions formed and called for the right to vote.

The new electoral law only allows security forces and members of the army to vote in municipal elections. Police and soldiers are barred from participating in election campaigns or attending public meetings.

Some 36,055 soldiers and security agents are registered to vote, according to Mehdi Jalouali from Tunisia's Independent High Authority for Elections (ISIE).

Most police unions have called for participation in the vote, but one organisation has called for a boycott.

"The security institution is at the disposal of the people and it must be neutral, with this vote it will not be," said Chokri Hamad, spokesman for the National Union of Interior Security Forces.