Tens of thousands of demonstrators are converging on the Belgian capital to protest government policies that will extend the pension age, contain wages and cut into public services.

Thursday's march through Brussels opens a month-long campaign against the free-market liberal coalition and will be capped with a nationwide strike on Dec. 15.

The government says it is forced to push through stringent austerity measures to keep the budget deficit within European Union constraints and insists businesses need more lenient tax policies to become more competitive in the global market.

The trade unions say government policies only target the workers with extended pension age limits, a freeze of the automatic link between wages and inflation and cuts in public services which will hit the population as a whole.