The Force Ouvriere union is calling for a co-ordinated response from workers
The French government has proposed measures to raise the number of older people in the workforce, in an attempt to tackle its ageing population.
Companies could be threatened with penalties if they do not increase their number of staff aged 55 to 64.
But the most controversial reform is for employees to work 41 years, not 40, to qualify for a full state pension.
Union leaders met Labour Minister Xavier Bertrand on Monday but there are already calls for strikes on 15 May.
France has one of the lowest rates of employment of workers aged 55 to 64 in the European Union, but also has one of the highest rates of life expectancy, at 84.5 for women and 77.6 for men.
55-64s IN WORK IN EUROPE
EU average: 44.7%
Source: Eurostat 2007
Although President Nicolas Sarkozy's government has decided not to push for companies to have a quota of older workers, it does want businesses which have not signed an agreement by 2010 to face extra pension contributions.
An estimated 400,000 people aged 57 or more are out of work and receiving unemployment benefit in France.
In 2003, the government introduced plans to require workers to have 40 years of employment before taking a full state pension. That was to be raised to 42 years by 2020.
The secretary general of the Force Ouvriere union, Jean-Claude Mailly, said that extending the number of working years to qualify for a pension to 41 years by 2012 amounted to "working longer to earn the same".
He called for a co-ordinated response from workers on 15 May, the day on which a teachers' strike is already scheduled to take place.
Attempts to reform the pensions system in France prompted waves of strikes across the public sector in 2003 and 1995.