(Reuters) - The U.S. Federal Trade Commission said it filed a complaint in a district court accusing Endo International Plc (>> Endo International PLC) of violating antitrust laws by striking "pay-for-delay" deals to block access to generic copies of its drugs.

Pay-for-delay settlements hurt consumers by delaying the entry of cheap generic versions of branded drugs.

The case is the first by the antitrust regulator that challenges an agreement not to market an authorized generic.

Endo's stock was down about 6 percent at $26.67 in morning trading on Thursday.

Settlements between drug firms that include deals like this harm consumers twice - first by delaying the entry of generic drugs and then by preventing additional generic competition in the market once a generic has entered, FTC Chairwoman Edith Ramirez said.

The FTC's complaint alleges that Endo paid the first generic companies that filed for FDA approval – Impax Laboratories Inc (>> Impax Laboratories Inc) and Watson Laboratories, a unit of Allergan Plc (>> Allergan, Inc.) – to eliminate the risk of competition for two of its branded pain drugs, Opana ER and Lidoderm.

The agency has reached a settlement with Endo's partners, Teikoku Seiyaku Co Ltd and Teikoku Pharma USA Inc, who were involved in the Watson deal, it said on Thursday.

(Reporting by Natalie Grover in Bengaluru; Editing by Anupama Dwivedi)