MPs would have to reveal more details of expenses claims under the system
A move to exempt MPs from having to publish details of expenses claims has been criticised as "outrageous".
The plan, announced by the government this week, effectively nullifies a High Court ruling that every receipt claimed by MPs should be published.
Instead Harriet Harman said expenses would be provided in "an affordable and appropriate way", under 26 headings.
Labour MP David Winnick told the BBC he was "unhappy" with the move in case it suggested MPs had "something to hide".
Last year campaigner Heather Brooke and journalists Ben Leapman and Jonathan Ungoed-Thomas won a lengthy Freedom of Information battle to get 14 MPs' expenses, including receipts, published in full.
The Commons authorities, which had spent £150,000 fighting the decision, said they would publish all MPs' claims and receipts in October.
But that deadline was missed as officials complained that the process of scanning and redaction, estimated to cost £950,000, was proving more complex than anticipated.
Ms Brooke said the Commons authorities had refused several of her FOI requests on the basis that all information would be published in October.
But announcing the new plans on Thursday, Commons leader Harriet Harman did not mention receipts or the Freedom of Information cases.
She told MPs the plans to break down expenses claims into 26 headings, rather than the current nine, would give the public "more information than they ever have before".
It would mean second home allowance claims would be broken down into mortgage interest claims, rent, hotel costs, council tax payments and "fixtures, fittings and furnishings" and repair cost claims, among others.
Ms Harman told MPs: "We want to make sure that the public have confidence that there are clear rules and they know what is going on."
But she said people had to be given the information in an "affordable and proportionate" way.
However FOI campaigner Ms Brooke told the BBC that by introducing changes to the publication of expenses as a statutory instrument, the government was effectively changing the Freedom of Information act, she said.
"It's a way to change the law without having a public debate," she said.
She added: "I think it's just really outrageous."
"This is the problem with the Parliamentary system - if they don't like the law, they can just change it, unlike the rest of us."
And Labour backbencher David Winnick told BBC Radio 4's World at One programme he was "somewhat unhappy".
He said his claims were all legitimate and he had no reason to think any other MPs were not.
But he added: "It's the perception. What I'm afraid of is what's being proposed could give the impression that we have something to hide and that would be, to say the least, very unfortunate indeed."
MPs' expenses have been scrutinised since Tory MP Derek Conway was reprimanded for his use of allowances to pay his son, who was a full-time university student at the time.
The months that followed saw Freedom of Information battles over MPs' expenses, the publication of the so-called "John Lewis list" against which MPs' claims are measured, and a Commons review of the system.
In the end MPs voted to keep their second homes allowance and rejected external auditing, but agreed to limit the amount they spend on furnishings to £2,400 a year.