Labour leaders have called on all public and private sector workers to observe a one-day stoppage and to attend one of the 190 protest rallies organised around the country.
Bernard Thibault, the leader of France's biggest union CGT, predicted on Europe 1 radio that the mobilisation could be "the biggest social event in years," and said he expected an "exceptional day," with an even higher turnout than June, when more than 800,000 took part in a similar day of action.
Turnout will be closely scrutinised - and probably subject to dispute - as a measure of the level of opposition to the pension reform bill. The law would increase France's minimum retirement age from 60 to 62 by 2018, which is still early by international standards, but would reverse a cherished and emblematic Socialist reform.
Prime Minister François Fillon, a Sarkozy ally, admitted that he expected "a strong turnout" by his government's opponents, but the president's supporters insisted that the reform must go ahead to reduce France's public deficit.
Widespread disruption is expected in transport, government, industry, banks and postal services. Just two out of five TGV high-speed trains are running, with reduced service on many other lines, according to state railway operator SNCF. But Eurostar trains between Paris and London are set to run normally.
Meanwhile, the DGAC aviation authority warned up to a quarter of flights into and out of Paris airports could be cancelled or delayed, although long-haul services are not expected to suffer greatly.
An Obea/Infra Forces opinion poll published on Monday showed 73 percent of French voters in support of the protest marches. But the survey also indicated that 65 percent thought the government would not change course.