The protesters say that they are taking action because the new government's coalition accord is unclear when it comes to the future of the railways. They are also unhappy with operations affecting the rail company's budget. Trade union representatives failed to convince train drivers not to join the unofficial action.
Three out of four train drivers joined the protest. Trades unionists occupied the rails for a while in Liège preventing all traffic for three-quarters of an hour.
Services from Ostend, Knokke and Blankenberge to Eupen, Hasselt and Tongeren were running. There's a service from Brussels to Leuven too, but traffic in the opposite direction, from eastern Belgium to Brussels and beyond, is problematic.
The rail occupation in Liège stopped at 8:45, but disruption in the Liège area is still significant.
International services have been disrupted too. A Thalys service from Liège to Paris was held up by the occupation. There are delays on the Liège - Aachen service too.
Belgium's publicly owned rail operator NMBS has asked passengers to check their website before travelling.
Tuesday's action follows a walk-out in Charleroi on Monday. A hundred services were cancelled. The line Charleroi - Brussels was most badly affected.