PARIS- Tunisia's state grains agency has asked one of its suppliers to avoid French wheat due to continuing strikes at French ports which have hampered recent shipments, raising concern in France that it may lose sales.

Public transport strikes that have crippled rail services and rolling stoppages by dock workers have left grain exporters in France, the European Union's biggest grain producer, struggling to get their supplies to ports.

The French grain industry warned last week of a severe impact on the cereals sector if strikes over pension reform that started early December were to last. Another 24-hour port stoppage has been called for Wednesday.

In a fax addressed to trading company Casillo Commodities Italia and posted on Twitter, Tunisia's Office des Cereales (ODC) asked the trading house to avoid France as a source origin when fulfilling a sale of wheat from west Europe.

"Having regard to the situation prevailing at the moment in French ports following the hardening of social movements in France ... you are requested to take all your provisions to avoid, exceptionally, this origination, although it is contractual, and this (is) in the interest of both parties," the Supply Director at ODC said in the letter dated Jan. 28.

ODC buys large volumes of grains in international tenders but it specifies regions from which the grain is to be supplied such as west Europe or the Black Sea region, rather than individual countries.

"It casts doubt on the French origin because buyers, be it the state offices, the millers and ultimately all buyers of goods, cannot afford to be unsure that they will be delivered," a senior trader involved in the last sales to Tunisia told Reuters.

"There are quite a few people who are starting to look elsewhere," he said.

Casillo is one of Tunisia's regular wheat suppliers. The sale cited was part of a tender in December in which the firm had sold two consignments of 25,000 tonnes of soft wheat.

The tender specified several shipment periods, depending on the origin of the soft wheat, between Jan. 10 and Feb. 25. 

The issue of whether to load in France was thought to concern one of the 25,000 tonne cargoes, the trader said.

"We will have to see what happens," he said.

"In its letter the office does not formally ban French wheat but is asking the exporter to avoid the origin in the current circumstances."

(Reporting by Sybille de La Hamaide; additional reporting by Michael Hogan in Hamburg; editing by David Evans and Alexandra Hudson) ((Sybille.deLaHamaide@thomsonreuters.com; +331 4949 5145;))