The unions are planning five days of industrial action, though three strike days at the end of January have now been moved to a later unspecified date out of concern Belgian students would not be able to attend their exams. The dispute centres on a new collective labour agreement setting out pay and working conditions and demands for a 4% a year increase in productivity at the state-owned enterprise.
The unions are keen to see the appointment of a social mediator after talks with the rail management broke down.
Representatives of the Flemish and Francophone wings of the socialist and Christian rail unions attended a meeting in Brussels on Monday but parted without any decision on next week's planned strikes.
Union sources say that the strike on 6 and 7 January can still be called off. It can be axed until 48 hour before it is planned to start.