OTTAWA -- Federal cabinet ministers were on the defensive Wednesday as opposition parties hammered proposed changes to the law that gives Canadians access to government files.

The criticisms largely echoed those voiced last month by the federal information watchdog, who said the Liberals' plan to amend the Access to Information Act would take people's right to know backwards.

The Liberals say their proposed access legislation, introduced in June, will raise the bar on openness and transparency following years of inaction by the previous Conservative government.

That was the message Treasury Board President Scott Brison, who is responsible for overseeing the act, and Democratic Institutions Minister Karina Gould delivered to the House ethics committee Wednesday.

"As we developed these reforms, we were guided by the principle that government information belongs to the people we serve," Brison told committee members. "We remain committed to this principle."

But opposition MPs zeroed in on proposals that would let an agency refuse to process an access request unless it identified the specific type of record, the subject, and time-frame.

Conservatives and New Democrats noted that Information Commissioner Suzanne Legault has called the proposed criteria unreasonable, and they expressed concern the clause would be abused.

Brison said the measure was intended to prevent "frivolous or vexatious" requests that are made in bad faith and often "gum up" the access to information system.

But he refused to say who would determine whether a request meets the criteria, and a senior Treasury Board official testified that less than one per cent of current requests are considered frivolous.

Brison opened the door to amending the proposed changes, saying the government "does not want requests rejected or denied by departments."

But opposition members accused the Liberals of ignoring years of recommendations from the ethics committee and information commissioner on ways to fix the law and make it easier to access info.

Brison and Gould were also forced to repeatedly defend the government's failure to make ministers' offices fall fully under the access law, as the Liberals had promised during the last federal election.

Ministers' offices will be required to regularly release certain records such as travel and hospitality expenses and contract information, but committee members said that isn't what was promised.

"I still wonder what the rationale would be for not extending the act as it was understood," Liberal backbencher Nathaniel Erskine-Smith said.

Gould said the government needed to protect ministers' ability to mull over and make decisions in confidence.

Brison lashed out at opposition members several times during his appearance, noting at one point that the Conservatives failed to update the 34-year-old access act during their 10 years in power.

And he accused the NDP of initially opposing Liberal proposals in 2013 to release information about MP expenses, when Parliament was embroiled in the Senate expense scandal.

The access act, which took effect in 1983, allows people who pay $5 to request everything from correspondence and studies to expense reports and meeting minutes.

Departments and agencies must answer requests within 30 days or provide a good reason why more time is necessary.

Many Canadians complain about lengthy delays in processing requests and blacked-out passages in the records that are eventually released.

Government departments can black out requested records on grounds related to national security, legal privilege, policy advice, commercial secrets, federal-provincial relations and other areas.

Records deemed to be federal cabinet secrets are completely off-limits for 20 years.