The former head of the American Humane Association's film and TV unit is suing her ex-employer and HBO, which aired the horse-racing drama "Luck."

Starring Dustin Hoffman, the show was canceled last March after a single season because of allegations of mistreatment of the animals on set. At least four horses reportedly died during production.

Barbara Casey said in a recently filed lawsuit she was wrongfully terminated by the AHA in January 2012 because she called attention to animal abuse on the show the AHA, HBO and Stewart Productions tried to cover up, The Hollywood Reporter said.

The lawsuit Casey filed in Los Angeles Superior Court alleges the AHA witnessed drugged, underweight and/or sick horses and knew the show's producers were misidentifying horses so animal safety representatives couldn't follow their medical histories, the entertainment industry trade newspaper said.

However, HBO has vehemently denied the allegations.

"We took every precaution to ensure that our horses were treated humanely and with the utmost care, exceeding every safeguard of all protocols and guidelines required of the production. Barbara Casey was not an employee of HBO, and any questions regarding her employment should be directed to the AHA," the cable TV network said in a statement to The Hollywood Reporter.

The newspaper said the AHA did not immediately respond to its request for comment regarding the lawsuit.