Franco-German drugmaker Aventis has taken legal steps in the United States against Sanofi-Synthelabo's hostile takeover bid.
"Aventis is lodging a complaint to ensure that Aventis shareholders are provided with full and fair disclosure regarding the unsolicited offer and that Sanofi fully complies with the US federal securities law," Aventis said in a statement.
"The action states that Sanofi's public filings and public statements made in connection with its proposed tender offer contain significant omissions and misrepresentations," it said.
Aventis has said it is studying all options to fend off Sanofi's stock-and-cash offer and has invited Swiss rival Novartis into merger talks.
Aventis last week reiterated its rejection of Sanofi's offer in a US regulatory filing, after Sanofi's bid opened there.
No one was immediately available for comment at Sanofi.
The French government dashed any hopes it would be impartial in the takeover battle for Aventis, the Financial Timesreported.
Citing an unnamed senior French government minister, the FTreported it would be "impossible" for France to adopt a neutral stance - a condition Novartis has set for making a counter-offer for Aventis.
The paper quoted French Prime Minister Mr Jean-Pierre Raffarin as saying: "Vaccines are extremely important to the national interest. Aventis has been built along Franco-German lines and a merger with Sanofi is an extension of that logic. We want our concerns to be taken into account."