In a report on how council staff shortages will affect key services, the watchdog suggested that the current shortage could delay one-third of planning applications.
It stressed that this could jeopardise the government's house building targets and lead to an even smaller number of affordable homes, widening the social and economic divide between those able to access the housing market and those excluded.
But it acknowledged that councils, the government and its partners have taken some action on shortages by introducing a culture change programme to make the profession appeal to school leavers and graduates.
The commission's report on the planning system in 2006 proposed sharing staff between councils as a solution to recruitment issues.
Chief executive Steve Bundred said: "Some councils are already doing an excellent job putting robust plans in place to deal with potential future skills shortages.
"But all chief executives, leaders and senior management should follow the example of the best councils and act now to defuse this demographic time bomb."
However, an RTPI spokesman said: "This would be the outcome if no action were taken to prevent it, but action is being taken. Our data show that levels of people choosing to study planning are buoyant. Our main concern is that professionalism in the sector is maintained."