With regional variations, clubs are restricted to spending pounds 140,000 in total on players' salaries. The League chief executive, Mike Smith, said: "Each of the players on the five clubs has been issued with a temporary licence until mid-October."
Licences of individual players could be revoked if that is necessary to bring a club's total wage bill under the cap.
Previously clubs who exceeded the limit were allowed to maintain their entire squads while ensuring the 10 players for each game had a combined salary within the restriction.
"That's no longer allowed," Smith said. "If clubs exceed the cap, then players will be de-registered and no longer allowed to play for that club."
It might also be hard for the suddenly unemployed to join other top clubs. Most of the 13 teams fill half their bench with Americans and must also include two under-22 age group players.