French trade unions have threatened to strike in protest at the government's decision to cancel a holiday on 16 May.
Mr Raffarin urged the French to turn up for work on 16 May
State sector workers must turn up for work on the public holiday under a new law brought in to generate more tax revenue for healthcare.
It was created after the health system failed to cope with a 2003 heatwave that killed 15,000 elderly people.
Analysts say the unpopular move could harm the government's campaign for a "Yes" vote in the EU treaty referendum.
'Day of Solidarity'
Prime Minister Jean-Pierre Raffarin urged people to respect the law and turn up for work on the day, the traditional Monday off after the Christian festival of Pentecost.
"I ask that the law, approved by the parliament, be respected by all," Mr Raffarin said, reports news agency AFP.
"The day of solidarity is a call to brotherhood among all French people. It's an act of generosity by French society for itself, for its future."
The government expects to raise an extra 2bn euros (£1.3bn) in revenue for its cash-strapped healthcare system by asking people to work for nothing on the so-called "Day of Solidarity".
Unions say the measure unfairly targets state workers and is not a proper financial solution. Private sector companies get to chose which public holidays to follow.
"We refuse this principle of this day of free work," said Bernard Thibault, head of the communist-backed CGT union.
Opinion polls carried in French newspapers show a majority of respondents oppose cancelling the public holiday.
Some schools said they would remain closed on 16 May while the Socialist-run Paris regional government has given its 1,200 workers the day off.
The state-owned railway company SNCF came up with a creative alternative whereby it will give its staff the day off and in return ask them to work an extra one minute and 52 seconds each working day.
Not everyone was amused however.
"The SNCF is mocking everybody," said Nicolas Sarkozy, the popular head of President Jacques Chirac's governing centre-right UMP party.
"If they thought they were being clever, they blew it."