Cooper Laboratories filed a lawsuit against Rorer.

The suit, filed in U.S. District Court in Philadelphia, challenges the “poison-pill” rights being issued by Rorer Group. Rorer announced its “share purchase rights plan” on Feb. 7. In a letter to shareholders, Rorer’s chairman stated that the plan “should deter any attempt to acquire the company in a manner or on terms not approved by the board.” Cooper, which owns about 4.96% of Rorer’s stock, alleges in its suit that the effect of the rights is to deprive Rorer’s shareholders of the rights to receive and consider proposals for control of Rorer and to vest such rights solely in Rorer’s board of directors.