The U.S. Supreme Court on Mar. 31 agreed to hear an appeal filed by Teva Pharmaceutical Industries in a patent fight over top-selling multiple sclerosis drug Copaxone.

The move could deter generic manufacturers from introducing cheaper versions onto the market as soon as May.

By agreeing to hear the case, the news agency Reuters said the high court cast into doubt a July 2013 ruling by the U.S. Court of Appeals for the Federal Circuit in favor of two teams developing cheaper generic forms of Copaxone,.

One of the teams consisted of Novartis subsidiary Sandoz with Momenta Pharmaceuticals, the other linked Mylan and Natco Pharma.

The appeals court upheld some of nine patents involved in the drug, or portions thereof, but declared several invalid that saw patent protection expiring in May 2014 rather than September 2015.