Israel-based generics giant Teva has moved forward with the early launch of a generic version of Bayer‘s birth control pill, Yaz, in the US, prompting a lawsuit.

Teva received FDA approval for its generic version of Yaz, marketed as Gianvi, in April but said that it would only launch the drug from 1 July 2011.

The company said, however, that under the licensing agreement between Bayer and Teva’s Barr Pharmaceuticals, the product could be launched earlier under certain conditions.

Bayer deny this and have said in a statement that the earlier-than-expected launch “constitutes an act of infringement of the relevant intellectual property,” and have filed a lawsuit in Delaware.

Yaz, over which Bayer has also sued both Novartis and Sandoz for making generics, had US sales of $782m in 2009.