Mayne Pharma Group (ASX:MYX) rejected claims by Cosette Pharmaceuticals that a material adverse change has occurred under their scheme implementation deed (SID), according to a Wednesday filing with the Australian bourse.

In February, the company said it entered a scheme implementation deed to be acquired by Cosette via a scheme of arrangement for AU$7.40 per share.

On May 17, Cosette issued a notice that the obligation under the SID for both parties to engage in good faith consultations for 10 business days has been triggered, the filing said.

The company responded that the claims do not meet the SID's definition of a material adverse change and that all relevant information had already been disclosed, the filing added.

Cosette has not terminated the deal but has indicated it may do so if the consultation period does not resolve the matter, the company said.

The company maintains that no consultation is required, but remains open to discussions and will continue to share information with Cosette as required under the SID.

Shares of the company fell almost 30% in recent Wednesday trade.