* Belgian, German, Luxembourg farmers join French-led strike
* French union says 30 pct of producers not delivering milk
(Adds detail on strike in France)
By Philip Blenkinsop
BRUSSELS, Sept 11 (Reuters) - Dairy farmers across Europe held back milk on Friday in a growing industrial dispute over low prices which could limit supplies next week.
Farmers from Belgium, Germany and Luxembourg joined French counterparts, who announced plans to strike on Thursday, the European Milk Board (EMB) said.
A group of Belgian farmers flooded a main square in the southern city of Charleroi with milk on Friday morning as part of the protest that has also included blocking roads and preventing trucks from picking up milk.
Dutch and Italian farmers were also considering action, an EMB spokeswoman said.
In France, dairy union the OPL said 30 percent of producers had joined the strike, with processors only able to collect about half of the normal volume of milk in parts of major producing regions in the west and north of the country.
"In some areas, dairies have been collecting even when it's not the normal collection day. That proves they're afraid of a milk shortage," the OPL said in a statement.
The OPL and fellow dairy union APLI launched the French strike on Thursday at a gathering of EMB members in Paris. [ID:nLA173201]
Milk producers want the European Union to drop plans to increase annual production quotas in order to boost prices to the 40 euro cents a litre level they say is needed to their cover costs and generate a basic revenue.
After a price spike in 2007, global dairy markets have deteriorated sharply over the past year, with European producer prices falling to lows around 20 cents a litre, fuelling protests by farmers across in several European countries.
A 10-day milk strike in Germany, Belgium, the Netherlands, Switzerland and Austria last year led to local milk shortages, the EMB said.
In Brussels, hundreds of farmers drove tractors into the city before a June EU summit, causing traffic chaos, and they returned this week to protest at the latest meeting of EU farm ministers.
The European Commission, which administers and regulates farm policy for the European Union's 27 member countries, has dismissed the idea that the milk quota system, due to expire in 2015, is to blame for weak prices.
Commission officials say EU milk production is expected to be between 4 and 5 percent below maximum quotas this year.
The Commission has already taken a series of steps to shore up dairy markets, including reinstating export subsidies and private storage.
It has raised ceilings on volumes of butter and skimmed milk powder that can be bought into public intervention stores, to remove supply from the market.
(Additional reporting by Gus Trompiz in Paris; Editing by Andy Bruce)