NSW courts have refused less than 2 per cent of police applications for secret recordings, reigniting claims judges are "rubber stamping" privacy intrusion, new data shows.

Only six out of 363 applications for surveillance device warrants were rejected in the first half of 2014. This was an increase from no refusals, out of 878 applications, in the prior 12 months.

Catherine Burn, Deputy Commissioner of Specialist Operations.

"The very low rate of refusals suggests either that applications for surveillance device warrants by NSW police are consistently of an almost perfect standard, or that the process of approval lacks rigour," said shadow NSW attorney-general Paul Lynch.

"In light of evidence recently in the Legislative Council, this is of great concern. There needs to be a proper review of this process."