A lawsuit has been filed against Valve Software that accuses the Steam platform-holder of enabling an "illegal online gambling market" via Counter-Strike: Global Offensive.

The suit, filed for CS:GO player Michael McLeod, claims that Valve "knowingly allowed, supported, and/or sponsored illegal gambling by allowing millions of Americans to link their individual Steam accounts to third-party websites."

It refers to websites like CSGO Diamonds and CSGO Lounge, where players can bet on match outcomes using weapon skins.

Because skins can be bought and traded for real money, these websites treat them "like casino chips that have monetary value outside the game itself because of the ability to convert them directly into cash," the suit alleges.

Furthermore, the suit adds that some such sites "[allow] minor users to place illegal bets," thanks to a lack of age verification.

Business journal Bloomberg ran a story in April that claimed these betting sites were part of a US$2 billion business.

"In sum, Valve owns the league, sells the casino chips, and receives a piece of the casino’s income stream through foreign websites in order to maintain the charade that Valve is not promoting and profiting from online gambling, like a modern-day Captain Renault from Casablanca," the suit says.

Real-money skin trading came to CS:GO in 2013's Arms Deal Update, which promised players they could "experience all the illicit thrills of black market weapons trafficking without any of the hanging around in darkened warehouses getting knifed to death."

McLeod is seeking unspecified damages and class action status in his lawsuit.