Betting firms Ladbrokes, William Hill, and PT Entertainment have agreed to change online games promotions after pressure from the regulator.
The Competition and Markets Authority (CMA) said punters must be able to cash out when they want, and not have to play more to release winnings.
It said that "gambling firms must now stop unfair online promotions that trap players' money".
The changes will apply to all promotions.
After a CMA investigation into whether the sector was breaking consumer protection law, three companies - Ladbrokes, William Hill, and PT Entertainment - will make changes to bonus promotions for online games such as roulette and poker.
Players will not be required to play multiple times before they can withdraw their own money
Gambling firms must ensure that any restrictions on gameplay are made clear to players, and cannot rely on vague terms to take players' money
Gambling firms must not make players take part in publicity to collect winnings