Information Commissioner Angelene Falk has received 2947 privacy complaints in the past financial year, along with almost 20,000 inquiries about privacy rights.

Ms Falk has initiated 21 investigations into serious and repeated data breaches over the past year, including an ongoing inquiry into Facebook.

The investigation is centred on the unauthorised release and use of the personal information of more than 300,000 Australian Facebook users.

The social media giant is due to provide more information in mid-November and the investigation is due to conclude early next year.

"It's a very significant matter for my office and the community," Ms Falk told a Senate estimates hearing in Canberra on Monday.

Facebook faces a maximum penalty of $2.1 million.

Her office has also been asked to review 801 freedom of information decisions in the past year, an annual increase of 27 per cent.

In the first quarter of 2017, the watchdog examined 168 FOI decisions, which rose to 281 reviews in the first quarter of this year.

Complaints and requests to the Office of Australian Information Commissioner have been climbing significantly year-on-year for the past three years.

Ms Falk acknowledged funding constraints were making it more difficult for her 88 full-time equivalent staff to perform their duties.

Ms Falk's office is also responsible for policing a new mandatory data breach scheme established in February.

Businesses and agencies must reveal data breaches when they occur, in cases where the personal information involved is likely to result in serious harm.

Individuals affected are then told what steps they must take in response to the breach.

Ms Falk received about 100 data breach notifications per month in the early stages of the scheme.

The watchdog was initially finalising 99 per cent of these cases within two months, but its response time has deteriorated slightly, with 87 per cent of notifications now wrapped up within 60 days.

Australian Associated Press