Real Betis claim refereeing mistakes have cost them all season and have complained to the Royal Spanish Football Federation (RFEF) and to the country's Referees' Committee (CTA).
Sunday's 2-1 defeat at Real Madrid was the latest match in which the Andalusian club felt refereeing errors went against them.
"The club has called the federation, we will continue to call [RFEF president Angel Maria] Villar and [CTA president Victoriano] Sanchez Arminio to protest because there have been too many games and too many decisions that have gone against us," Betis vice-president Miguel Lopez Catalan said to his club's official TV channel. "We don't want gifts from them and we don't want to be at a disadvantage."
Betis were unhappy with referee Mateu Lahoz's performance during the encounter at the Santiago Bernabeu, believing he should have sent off Madrid goalkeeper Keylor Navas in the first half.
With the score 0-0 in the 21st minute, Betis player Darko Brasanac was sent through on goal and was brought down by Navas on the edge of the area, in what the visitors argued was a last-man offence.
Betis believe Navas should have been shown a red card but Lahoz waved play on and Madrid went on to win 2-1 to return to the top of La Liga.
"We are extremely angry," Lopez Catalan said. "I think everyone saw it, even the official. It was a clear red but he didn't want to make the call. That episode would have changed the game. Madrid doesn't need those gifts."
According to Marca, Sunday's game was one of nine La Liga encounters in which Betis have been hindered by refereeing mistakes.
Betis, coached by Victor Sanchez del Amo, have won just one of their last 10 league games and are 14th in La Liga, nine points clear of the drop zone.
"We are playing well and we need to persevere because in the end the results will come," Lopez Catalan said. "There are still many games left to play and the important thing is that the team is growing. Now we have focus on our game at home to Osasuna, we need a win at all costs."
Betis, who finished 10th last season after returning to Spain's top flight, host rock-bottom Osasuna on Saturday.