Queens Park Rangers revealed they have begun legal proceedings against the Football League, a day after being relegated from the Premier League.
The club say they are challenging "the legality of the Championship Financial Fair Play rules", which could leave them facing a fine of up to £58m.
Rangers said any charge for breaching the rules would not begin until the outcome of their challenge was known.
Their relegation was confirmed by Sunday's 6-0 loss at Manchester City.
In March, the club announced losses of £9.8m, but £60m worth of loans were written off by owner Tony Fernandes and other shareholders.
A failure to pay any fine imposed could see the London side being refused entry into the Championship.
|Football League Financial Fair Play|
|Championship clubs were permitted losses of £8m (£5m funded by shareholders) in 2013-14.|
|Clubs promoted back to the Premier League who exceeded those losses are subject to a fine.|
|There is a sliding scale on the next £10m of losses, with a maximum fine of £6.681m.|
|Once losses exceed £18m, the fine is imposed on a strict pound-for-pound basis.|
|Should there be an overall loss of £30m, the fine would be almost £19m. If it was £50m, the figure would be nearly £39m.|