PARIS, April 10, 2008 (AFP) - Police investigating claims that French businesses for years secretly funded their trade union adversaries on Thursday raided the Paris headquarters of the country's top employers' federation.

The Medef federation issued a statement saying it was "cooperating fully with legal authorities to help them shed light on the UIMM (metal and mining lobby) affair."

The powerful UIMM, a member of Medef, has been under police investigation after it was revealed that some 19 million euros (30 million dollars) in cash had been withdrawn from UIMM accounts since 2000.

A source close to the probe said Thursday that the investigators were in particular looking for emails between the Medef chief Laurence Parisot and other Medef members concerning the system of UIMM cash withdrawals.

The raid came a day after a former president of the UIMM, Daniel Dewavrin, was placed under investigation in the affair.

The UIMM's head Denis Gautier-Sauvagnac was forced to step down and placed under investigation over the revelation in September that some 19 million euros had been withdrawn.

Investigators believe they have stumbled on hidden "war-funds" used by the century-old metals federation to subsidise trade unions and "buy" agreements to end industrial disputes, in an arrangement reaching back decades.

They are also looking into suggestions of illicit political party funding, with the questioning in February of a former intelligence chief who alleged the UIMM helped pay for Valery Giscard d'Estaing's presidential campaign in 1974.

Shock over the revelations turned to outrage when it emerged that the UIMM offered its disgraced ex-boss Gautier-Sauvagnac a 1.5 million euro severance package.

The affair has led to a fierce battle of wills between would-be reformers and a powerful industrial old guard. It pits Parisot against the UIMM, Medef's most powerful branch, whose 45,000 members include the carmaker Peugeot Citroen and the nuclear giant Areva.

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04/10/2008 15:32 GMT