The thorny issue of secularism has again divided France following the authorities' instructions to fly flags at half-mast in honour of the Pope.
The French flag symbolises the republic's secular traditions
Interior Minister Dominique de Villepin also urged top regional officials to attend Mass on Friday - the day Pope John Paul II will be buried in Rome.
The government has been accused of double standards, since overt religious symbols are now banned in schools.
France has traditionally insisted on a strict separation of church and state.
The government ordered that the tricolour be lowered on France's public buildings for 24 hours after the announcement of the Pope's death.
Flags will again fly at half-mast on Friday.
Many are grieving for the Pope in France, where surveys suggest about 60% of people are Catholics.
Mr De Villepin insisted on Tuesday that flying flags at half-mast was "established custom" for the French republic.
"This has happened for every pope under the Fifth Republic, and the Fourth and Third Republics," he said.
But the Deputy Mayor of Paris, Green Party member Christophe Girard, said he was "troubled" by the decision.
"On the front of our town halls, our schools, it is marked 'Liberty, Equality, Fraternity'. It isn't written 'Catholic France' or 'the Catholic Republic of France', like the Islamic Republic of Iran."
Socialist Senator Jean-Luc Melanchon said the government's move was "a sort of favour made to one religion".
"The state authorities must demonstrate an absolute secularism without shades or half-tones," he insisted.
Pressure to protect France's secular traditions prompted the state to ban conspicuous religious symbols - including Muslim headscarves - from state schools last year.
Newspapers have devoted much space to the flag issue, with readers' letters for and against the government's instructions.
French President Jacques Chirac - one of many world leaders travelling to Rome for the funeral on Friday - has postponed until 14 April a televised debate on the EU constitution that was originally planned for Thursday.