Just ACOD members downing tools will probably be enough to cause considerable disruption (see below), but ACV Transcom is now covering for workers that would like to join to strike. They have the free choice to participate in the rail strike or not. The socialist (ACOD) and Christian (ACV) trade unions are by far the two biggest players. The third one, the liberal ACLVB, is much smaller.
Earlier, the ACOD announced a general strike in the public sector for 22 April to protest against the policy choices made by the different governments, and more in particular the new round of cuts in the public sector, the "attacks" on the pensions and the working conditions for civil servants.
The ACV and ACLVB announced that they wouldn't join the action, but now the ACV is opening the door for its members to join the rail strike. A similar strike was held on 30 June last year (with then only the ACOD participating). This led to 4 in 5 train services being scrapped or disrupted and only 1 in 5 running according to schedule.
All public services are expected to be hit to a bigger or smaller extent anyway.