Thousands of people from across the EU are expected to march in Brussels to protest against sweeping austerity measures by many national governments, according to BBC.
The European Trade Union Confederation says its protest could be one of the biggest in Belgium`s capital for years.
The union says EU workers could become the biggest victims of a financial crisis set off by bankers and traders.
A general strike has begun in Spain and protests are planned in Greece, Poland, Italy, Latvia, Ireland and Serbia.
Many governments across the 27-member bloc have been forced to impose punishing cuts in wages, pensions and employment to deal with spiralling debts.
In Greece and the Republic of Ireland, unemployment figures are at their highest level in 10 years, while Spain`s unemployment has doubled in just three years.
In Britain, the government is planning to slash spending by up to 25%, while France has seen angry protests against a planned increase in the minimum retirement age.
Labour unions in Spain have started a general strike by marching through the capital, Madrid, in an effort to shut down the city. There has been mass picketing outside bus and metro stations since midnight. There were also protests in Barcelona.
The European Trade Union Confederation (Etuc) says it hopes that about 100,000 people from some 30 countries will take part in the Brussels march, which is due to begin at 1100 GMT.
Etuc says the protesters will be marching on EU institutions to voice their anger over budget-slashing plans and cuts which "could lead Europe into a recession".
The union warns that the financial crisis - which it describes as the worst in Europe since the 1930s - has already made 23m people across the EU jobless. It fears that the austerity measures being implemented by various EU government could "result in even more unemployment".
"We didn`t cause this crisis. The bill has to be paid by banks, not by workers," Etuc said.
Instead, the union urges governments to guarantee workers stable jobs, strong social protection and better pensions.
Workers in many EU countries are frustrated that they are paying for the mistakes of the banks and the financial sector, the BBC`s Christian Fraser in Brussels reports.
The recovery is still fragile. In some countries it has not even begun, and many fear the cuts could provoke further trouble, our correspondent says.
He adds that in short, it is a debate on austerity versus stimulus, cuts or spending, and the opinions are deeply and bitterly divided.