The issue relates to compensation for players injured while on international duty.
The G14 - made up of 18 of Europe's most powerful clubs - is backing Charleroi's claim for financial help after Abdelmajid Oulmers was out for eight months when he tore ankle ligaments playing for Morocco.
The Charleroi midfielder was injured in a friendly against Burkina Faso last November and missed the rest of the season.
G14 general manager Thomas Kurth told the organisation's official website: "In March 2004, G14 filed a complaint with the Swiss Competition Commission (COMCO) claiming violations of Swiss competition law committed by FIFA in adopting and using the same regulations cited by Royal Charleroi.
"As it is G14's wish to seek a once and for all clarification if these regulations are legal, it is sensible for us to join this case."
FIFA, which refuses to negotiate with the G14, has always maintained it is up to national associations to reimburse clubs for players on international duty and is not the responsibility of the world governing body.
FIFA says 75 per cent of the profits from major tournaments such as the World Cup are ploughed back into the national associations who decide themselves what to do with the money.
The legal case brought by Charleroi officially opened on Monday and G14 has joined the proceedings by filing an 'application for voluntary intervention'.
A statement on the G14 website said: "G14 becomes a full party in the proceedings before the Charleroi Commercial Court ... in a complaint about the illegality of Articles 36 ... of the FIFA regulations which oblige clubs to make players available for national team duty under conditions unilaterally imposed ..."
