Belgian farmers flooded a main square in the city of Charleroi with milk, and blocked roads and prevented trucks from picking up milk.
Dutch and Italian farmers were also considering action, an EMB spokeswoman said.
In France, the OPL dairy union said 30% of producers had joined the strike, leaving processors collecting only about half of the normal milk volume in major producing regions. Some German and Dutch milk producers said they supported the French call, but were barred by law from strike action.
The EMB want the EU to drop plans to increase quotas — even though Commission officials predict milk production will be 4-5% under quota this year.