Valve is no longer permitting gambling sites to use its technology.

The company, which owns and operates the Steam distribution portal and popular games like Counter-Strike: Global Offensive, announced today that it is enforcing the rules of its Terms of Service for the application protocol that enabled gambling sites to operate. It will request that all gambling sites, like CSGO Lotto, Skings Gambling, and CS:GO Diamonds, to stop immediately.

Up until now, these sites have used the OpenID API (application protocol interface) to enable item-trading between a pool of players. Everyone could wager their various digital items — some worth upward of $1,000 — and then the winning team would take the spoils.

“Using the OpenID API and making the same web calls as Steam users to run a gambling business is not allowed by our API nor our user agreements,” Valve spokesperson Erik Johnson wrote in an update. “We are going to start sending notices to these sites requesting they cease operations through Steam, and further pursue the matter as necessary. Users should probably consider this information as they manage their in-game item inventory and trade activity.”

GamesBeat has reached out to Valve for further comment, and we’ll update this post with any new information.

These operations recently came under scrutiny following the revelation that popular YouTube personalities Trevor “TmarTn” Martin and Tom “ProSyndicate” Cassell founded and own a stake in the CSGO Lotto site they promoted on their video accounts without disclosing that relationship. Last week, a mother of one player filed a complaint in the Southern District of Florida against CSGO Lotto, Cassell, Martin, and Valve alleging they collectively created a market that operates like an illegal casino.

You can read that complaint below:

Updated on July 13 at 3:30 p.m.: This story originally stated Valve changed its Terms of Service, but that is not correct. I’ve fixed the wording and apologize for the error.