The NBA warned a touring group of its stars that they could face financial fines for participating in clinics in Manila, Philippines, that include short scrimmages and games of "H-O-R-S-E," league sources told Yahoo Sports.

Several NBA stars, including James Harden, Kawhi Leonard and Damian Lillard, were scheduled to participate in promotional appearances in Manila this week, and the NBA has told its Players Association that the event organizers failed to gain league approval, sources said.

There were scheduled to be two days of exhibition events on Tuesday and Wednesday in Manila, but news reports out of Manila suggest that those events were canceled and ticket refunds were given to fans.

The NBA warned against violations that included "some kind of exhibition of basketball skills," including shooting games and dunk contests, an NBPA memo obtained by Yahoo Sports said.

In the memo, the Players Association informed player agents and players that the NBA "has taken the position that any such exhibition or competition is unallowable and is not approved for player participation under the [collective bargaining agreement], regardless of whether it is incorporated into a 'clinic' or other 'benign-sounding activity.'"

Player agents believe that the NBA took a hardline stance on the Manila event because it wants to keep financial control of these international events involving NBA players, selling its own sponsorships to organizers and controlling the payouts to players.

The NBA players cut a direct deal with the Manila organizers, including some star players earning $150,000-plus stipends for the two-day event in the Philipines, sources said.

A high-ranking league official told Yahoo Sports "our biggest concerns aren't sponsorships and payouts, but the playing conditions around the games – quality of the floor, equipment around the court, presence of doctors and facilities for treatment, etc."

The warning was delivered to a formidable group of NBA players that also included Kyle Lowry, Terrence Ross, DeMar Derozan, Tyson Chandler and Brandon Jennings, sources said.