Parliament's Government Administration Committee is concerned that a backlog of complaints with the Office of the Ombudsman could have a "chilling effect" on new complaints lodged with the Office.

In its Annual Review of the Office of the Ombudsman for the year to 30 June 2015, the committee says opposition members of Parliament wishing to avoid burdening the Office may be deterred from complaining about agency responses to Official Information Act requests.

"The Chief Ombudsman told us that the Office wants to change this perception of its capacity," the review says.

"Over the last three years, the Office has reviewed and restructured its complaints handling system to increase efficiencies. This has included strengthening its early resolution process, so that staff deal with simpler requests and complaints when they come in."

In the year to 30 June 2015 the Office received 12,151 complaints and other items of new work. This was the second highest amount ever received and 10% higher than the previous year. The Office did not meet its timeliness targets for completed complaints.

The committee also says it is concerned that staff caseloads are too high. While the Office has reduced caseloads to 35 cases person (down from 50 to 60 cases), the international standard to ensure adequate attention and followup is 25 cases per person.

The Office's rate of staff turnover increased to 21% in the 2014/15 year, which the committee says is high for an office of its size.