La Liga has filed complaints against Paris Saint-Germain and Manchester City to UEFA for "continuously breaching" financial fair play regulations.
The Spanish top-flight revealed that an initial complaint was made against the Premier League team in April, but has been followed up with another about the French giants.
La Liga argues that the two teams' "irregular financing" and big spending violates UEFA's rules and affects all European leagues and clubs.
What did La Liga say about Man City & PSG?
The league also cited a conflict of interests regarding PSG president Nasser Al-Khelaifi, given his role as European Club Association (ECA) chairman and his role as the organisation's delegate to UEFA's executive committee.
The statement read: "LaLiga this week filed a complaint with UEFA against PSG, which will join another against Manchester City in April, for understanding that these clubs are continuously breaching the current financial fair play regulations.
"LaLiga considers that these practices alter the ecosystem and the sustainability of football, harm all European clubs and leagues, and only serve to artificially inflate the market, with money not generated in football itself.
"LaLiga understands that the irregular financing of these clubs is carried out, either through direct injections of money or through sponsorship and other contracts that do not correspond to market conditions or make economic sense.
"The complaints against Manchester City before UEFA were made in April and this last week the one corresponding to PSG has been presented, although it is not ruled out that in the coming days extensions of some of these complaints will be made with the contributions of new data.
"Additionally, LaLiga has contracted law firms in France and Switzerland, including the French firm of lawyer Juan Branco, with the aim of undertaking administrative and judicial actions before the competent French bodies and before the European Union as soon as possible.
"In Switzerland, LaLiga is studying different representation options due to possible conflicts of interest of Nasser Al-Khelaïfi derived from his different roles in PSG, UEFA, ECA and BeIN Sports."
Is La Liga's complaint related to Haaland & Mbappe?
The Spanish league's appeal to UEFA comes in the wake of Erling Haaland's transfer to City and Kylian Mbappe's contract extension at PSG.
Mbappe had long been expected to join Real Madrid and the striker's mother said he had an agreement in place with the European champions.
However, he ended up committing to a three-year contract with the French club, much to the ire of Madrid and La Liga, which vowed to pursue legal action and file complaints to UEFA and the European Union.
Haaland, too, had been linked with a move to La Liga as Madrid and Barcelona had both been after him.
However, he ended up agreeing to join City in a deal worth £51 million ($63m) from Borussia Dortmund.
Man City, PSG & UEFA financial fair play rules
UEFA implemented the financial fair play rules to stop clubs spending more money than they earn and putting themselves in trouble.
City and PSG have both been the subject of investigations for allegedly violating the regulations.
UEFA initially banned the English team from European competitions due to "serious breaches", but the club appealed the punishment and it was subsequently overturned by the Court of Arbitration for Sport (CAS).
In 2014, both PSG and City were sanctioned by European football's governing body in the form of fines and restrictions on transfer spending.