Following a review of the service, the Assembly’s Public Accounts Committee has said it had "consistently failed" to meet targets, the BBC reports.
According to Committee chairman, Paul Maskey, the delay in handling major applications was a "particular concern" and while there had been a recent improvement, it was not enough.
"In the current economic climate more than ever, Planning Service has a pivotal role to play in developing the economy and it must focus on strategic applications which can make a real difference to social and economic wellbeing," said Mr Maskey.
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"These vital applications are still not being handled quickly enough."
The Planning Service's new electronic planning application system, which is now four years behind schedule and millions over budget, was also criticised.
Originally estimated at £5.5m, the costs have now sprawled towards £12.8m.
These latest findings come three months after the Northern Ireland Audit Office published a similar report, saying the Planning Service had failed to meet either its own or "public service agreement" targets in relation to the time it took to process applications.
However, the Audit Office did point out that staff caseloads in the NI Planning Service were considerably above the UK average.
(NS/GK)
