Atlético Madrid have mocked Real Madrid in a social media post ahead of Saturday's Madrid derby in response to Real's pressure tactics directed at officials.
Madrid, who have often been accused of complaining about refereeing decisions on their official TV channel, went further on Monday in the aftermath of their 1-0 loss at Espanyol when they sent a four-page open letter to the Royal Spanish Football Federation (RFEF) demanding "a total renewal of the refereeing system."
Atlético responded by posting a message on X that had an image resembling an Ikea assembly instruction guide headlined "basic instructions for the derby."
It included: "Using your official TV channel once again to press referees."
Atlético had highlighted what they viewed as intimidation by Madrid in a previous message on X, writing: "Friends of the RAE (Royal Spanish Academy in charge of the Spanish language), in recent days we are being asked a lot about a matter, and we don't want to make mistakes.
"Can you help us with the nuances of the following verbs? press, scare, intimidate, coerce, frighten, influence, impose. Thank you so much!"
Spain's Technical Committee of Referees (CTA) president Luis Medina Cantalejo, said "referees are honorable."
"I don't want to add more fuel to the fire," he said in an extract from an interview with El Chiringuito.
"My colleagues and I are not corrupt. We might be really clumsy, or really bad, but corrupt? No ...Despite all the letters, statements, no referee goes to a stadium with the idea of hurting anybody."
Barcelona coach Hansi Flick, meanwhile, was asked about Madrid's open complaint on Wednesday.
"This is their choice. They've done it like this and it's not our way. I said no excuses" he said.
"We will do it like that. Every coach, every club has some reasons to say something. We are humans and we all make mistakes.
"The referees have really a tough job and we have to take care about them. It's not easy this situation."
Madrid are one point clear of Atletico at the top of LaLiga heading into this weekend's game at the Bernabéu.