The Spanish league has summoned its member clubs to the United Arab Emirates on Dec. 7 with the aim of addressing "several important modifications to the statutes and internal regulations of LaLiga."
Madrid and Barca both responded on Wednesday, however, by saying they would not take part in the meeting as they continue their ongoing battles with LaLiga president Javier Tebas.
Madrid said they believed the forum was "illegal given clubs are being called to travel to a place that is more than 5,000km away from LaLiga's headquarters."
A statement from Madrid added: "It is completely unjustifiable to address in such an improvised and urgent manner, in the absence of the appropriate discussion and careful analysis, relevant modifications to LaLiga's internal regulations."
LaLiga had promised to provide clubs with transport and accommodation for the meeting, which also drew criticism from Madrid.
"It is completely inappropriate and deeply incoherent for LaLiga to undertake the economic expense of transporting more than 100 people to hold an event of this nature, at this time of year, in the United Arab Emirates, when it could be held at LaLiga's headquarters without involving excessive costs," their statement added.
"Clubs are going through very difficult times financially, burdened by the drop in income experienced in recent years, making it incomprehensible that excessive and unnecessary expenses should be incurred, in particular in the current economic climate."
A statement from Barca, released at the same time, said: "Extremely relevant business is on the agenda concerning the modification of LaLiga's regulations that requires prior debate and a more extensive and participatory analysis to come to the best consensus that such a wide-ranging reform deserves.
"Barcelona's position has always been that of reaching consensual agreements after having examined the issue coherently and respecting all positions.
"For that reason, we do not believe it is the right time to travel to Dubai for an event that could take place at LaLiga's headquarters and once again we show our opposition to any form of action that we consider damaging to the rights and interests of the club."
LaLiga responded later on Wednesday denying Madrid and Barca's "unfounded accusations" and accused the duo of trying to hinder the growth and development of other clubs in Spain.
A statement said the trip could "in no way be classed as illegal," was voluntary for clubs and was part of a larger excursion to the Middle East, similar to one they have done in India before, to help clubs grow internationally.
"With stops in Dubai and Doha, it is an opportunity to learn more about the region as well as to attend a World Cup game and an event that takes place in Dubai next week where various people from the footballing world are in attendance," the statement said.
"No club is obliged to travel to Dubai to participate in the assembly, since remote participation systems are in place, and they have been informed as such from the beginning."
There are a number of other factors aside from the meeting's timing and location which have led Barca and Madrid to boycott the summit.
A source close to Barca told ESPN that the club feel LaLiga chief Tebas' actions are often to the detriment of the Catalan club, in particular with reference to the financial fair play rules which govern Spain's top-flight and the European Super League.
Madrid and Tebas have also fallen out over several topics in recent years, including their attempt to create a Super League with Barca, the management of their television rights and the CVC deal LaLiga agreed last year, which Madrid and Barca also pulled out of.
In the period from 2015-2021 -- when LaLiga started the collective sale of television rights -- there were 51 legal actions brought against LaLiga by Madrid.
At the start of this year, 21 were ongoing, 23 had been decided in favour of LaLiga, five in favour of Madrid and two had been abandoned by Madrid.