Barcelona have filed a formal complaint with European governing body UEFA about the refereeing of Wolfgang Stark in Tuesday's 2-2 Champions League draw at Paris St Germain.
Barca were incensed that Zlatan Ibrahimovic's goal to make it 1-1 in the 79th minute of the quarter-final first leg in Paris was allowed to stand when the Swede was clearly in an offside position.
Ibrahimovic, who spent a season at Barca in 2009-10, was only playing after UEFA halved on appeal the two-match ban he received after his sending off at Valencia in the last 16.
"We have sent a letter to UEFA communicating our displeasure because the referee did not apply the rules in Paris," Barca spokesman Toni Freixa told a news conference after a meeting of the club's board on Thursday.
Barca host PSG in the return game at the Nou Camp on Wednesday.