The Spanish Football Federation (RFEF) says it is totally opposed to La Liga's plan to sell a 10 per cent in the league for £2.3bn to private equity firm CVC Capital Partners.
RFEF say the proposed deal will have serious implications for Spanish football and is "completely illegal" and "appalling".
La Liga clubs will vote on the deal at their general assembly on Thursday. Two thirds of the 42 clubs need to vote in favour for the deal to be ratified.
Real Madrid and Barcelona have already said they are opposed to the deal.
Real Madrid say they are talking legal action against La Liga president Javier Tebas and CVC Capital Partners to stop the deal.
"This agreement was reached without the involvement or knowledge of Real Madrid and today, for the first time, La Liga has given us limited access to the terms of the agreement," read a club statement released last Thursday.
"The clubs have signed over their audiovisual rights exclusively for their sale on a competitive basis for a period of three years. This agreement, by way of a misleading structure, expropriates 10.95 per cent of the clubs' audiovisual rights for the next 50 years, in breach of the law.
"The negotiation was carried out without competitive proceedings and the financial conditions agreed with CVC Capital Partners give them annual returns of over 20 per cent. This opportunistic fund is the same which tried and failed to reach similar agreements with the Italian and German leagues.
"Real Madrid cannot support a venture which hands the future of 42 Primera and Segunda División clubs over to a group of investors, not to mention the futures of those clubs who qualify over the next 50 years.
"Real Madrid will convene the Assembly of Representative Members to debate the agreement and discuss the significant loss of equity, unprecedented in our 119-year history."
Barcelona also expressed their opposition to the deal in a statement, which read: "FC Barcelona considers that the operation that has been announced has not been sufficiently discussed with the clubs [the owners of the TV rights]; that the amount is not congruent with the years of duration, and the deal affects part of all clubs' audiovisual rights for the next 50 years.
"The terms of the contract that La Liga is describing condemn Barcelona's future with regard to broadcasting rights.
"FC Barcelona wishes to express its surprise at an agreement driven by La Liga in which the teams' opinions, including those of FC Barcelona, have not been taken into account.
"There has not even been a presentation of options offered by other competitors in order to evaluate the pros and cons in a post-pandemic situation in which there are still many questions that are left unanswered."