That proposal is part of the president's wider plan to change the French economy, including decreasing union power, which he says it necessary to increase national competitiveness.
Strikes are also being held by other public sector workers, including employees at state energy companies and theatre workers, as well as the main student body, the UNEF.
Opinion polls suggest a majority of French people support the government's drive to change the so-called "special pension regimes" which allow some workers to retire at 50.
"I will carry out these reforms right to the end. Nothing will put me off my goal"
Nicolas Sarkozy, France's president
Send us your views
But other disputes are brewing and public discontent growing amid increases in the cost of living and rising petrol and housing prices.
Police used truncheons and tear gas to break up a separate student union protest at a Paris university hours before the strike began on Tuesday.
Sarkozy told the European Parliament during a visit to Strasbourg: "I will carry out these reforms right to the end. Nothing will put me off my goal.
"The French people approved these reforms. I told them all about it before the elections so that I would be able to do what was necessary afterwards," he said.
Xavier Bertraund, the labour minister, is preparing to meet union leaders on Wednesday.
Transport operators are expecting disruptions to extend into next week.
The "special regimes" were introduced after World War Two for workers in especially arduous jobs and allow some to retire after paying pension contributions for 37.5 years rather than the 40 years demanded of other employees.
The government says it will have to pump $7.3 billion (five billion euros) into the special pension funds this year alone to balance accounts and says an increase in contribution periods to 40 years for all workers is non-negotiable.
Transport workers say that although working conditions may not be as hard as when the system was devised more than half a century ago, they still suffer low pay and awkward working hours that justify their special status.