Sigma Pharmaceuticals Ltd (ASX:SIP) says it has been advised of a shareholder class action lawsuit over its alleged failure to disclose its financial position before a capital raising in September 2009.

The drug company said it had received correspondence foreshadowing a legal action for non-disclosure although the amount of the claim has not been quantified. It will "vigorously" defend itself should legal proceedings be commenced, Sigma said.

The Proposed Class Action will allege "Sigma engaged in misleading or deceptive conduct in relation to the guidance provided on 7 and 14 September 2009 by providing guidance concerning its NPAT for the year ending 31 January 2010, without reasonable basis; and Sigma breached its continuous disclosure obligations by failing to inform the market of information, of which it ought to have been aware throughout the period, including the significant deterioration in Sigma's share of the generic pharmaceuticals market to the extent that this varied from management's expectations."

Slater & Gordon has stated, "As part of these investigations, Slater & Gordon has been working with research analysts, investors and experts and believes there is a reasonable cause of action against Sigma on behalf of its shareholders."

In mid-August, Sigma announced it had agreed to sell its pharmaceuticals division to South African-based Aspen Pharmacare Holdings Ltd for $900 million.

Stocks in the pharmaceutical company were steady at 48.5 cents by 1308 Friday AEST.