The unions suspended their industrial action after Jean-Marc Janaillac quit his post a month ago when company employees voted against a two-percent pay rise this year and five percent in 2019-21, conditional on the company's performance.
But they have yet to receive a new offer and say they will strike again if interim boss Anne-Marie Couderc does not come up with a better deal than her predecessor offered.
The unions are calling for a five-percent rise this year, pointing out that workers have not received a general pay rise since 2011.
In a letter to the unions on Friday, Couderc promised to "concrete responses" on salaries at a works committee meeting next Thursday.
The unions say the strike could be called off or made tougher, according to what she proposes.