He has spoken of a possible "pause" once he raises the retirement age and changes some state sector pensions.
Fears about job losses, immigration and security, as well as resentment about issues such as bank bailouts and executive pay have all dented Sarkozy's popularity, which has fallen since he won approval for his handling of the financial crisis in 2008.
Sarkozy also needs to check France's public deficit, which is expected to reach 8.2 per cent of gross domestic product in 2010, something which could be more difficult if serious electoral losses undermine public support for change in the eurozone's second biggest economy.
The powerful CGT union has already called for a day of protest over wages and pensions on Tuesday. Other groups, such as farmers, may also see a big defeat for the centre-right as an opportunity to put pressure on the government.
There has also been increasingly open criticism of the leadership from within the
UMP, where some well-known party figures including Alain Juppe, the former prime minister, are calling for a change of course.
The centre-right suffered one of its worst losses in years in the first round of the ballot on March 14, with Sarkozy's party scoring just 26 per cent as the Socialists took 29 per cent and the broader left parties combined claimed some 50 per cent.
The Socialist opposition has called on its supporters to turn out in greater numbers to secure their regional bastions and begin the fight back that could see their divided party mount a credible challenge in 2012.
Regional councils in 25 regions, 22 on the French mainland and three overseas territories, are up for grabs, the Caribbean island of Guadeloupe having already been won outright by the Socialists in the first round.
The left already controls 20 regions in continental France, and a close race is expected in right-wing hold-outs, Alsace and Corsica.
High abstention levels, which saw more than half of voters stay at home, and a surge in support for the far-right National Front, which won almost 12 per cent, did not bode well for the government before Sunday's final run-off.
Polling opened at 8am local time (07:00 GMT) and will continue until 8pm.