Harriet Harman says expense claims need to be dealt with "affordably"
Campaigners have called on MPs to "stand up and be counted" against a potential rule change exempting them from Freedom of Information laws.
MPs are due to vote this week on the new rules, which would allow them to keep their expense details secret.
Now opponents have launched an online campaign, urging voters to put pressure on their local MPs to oppose the move.
By Monday afternoon an estimated 1,000 e-mails had been sent and organisers are confident the total will grow.
The e-mails were in response to an appeal earlier in the day from mySociety.org - a website with 75,000 subscribers that campaigns for more openness in politics.
In 2007 the group played a role in defeating a similar move by MPs to exempt themselves from Freedom of Information (FOI) requests.
The group says widespread opposition to the plans might convince MPs to vote against them.
MySociety director Tom Steinberg told the BBC: "We are a strictly non-partisan group, but we are using the internet... to spread the word that this exemption is unacceptable."
The rule change has been proposed by the Leader of the House of Commons, Harriet Harman.
Her parliamentary order, which MPs will debate on Thursday, aims to remove "most expenditure information held by either House of Parliament from the scope of the [Freedom of Information] Act".
It means under the law, journalists and members of the public would no longer be entitled to learn details of an MP's expenses.
Last week Miss Harman said information about expense claims needed to be given in an "affordable and proportionate" way in future.
Instead, she is proposing that MPs list their expense claims under 26 general headings, with no specific detail about what has been purchased.
The proposed rule change would destroy years of campaigning by journalists and others to force MPs to disclose detailed expenses.
It would also overturn a High Court ruling last year that would have resulted in all MPs being required to publish a breakdown of their expense claims on request.
Following the ruling, it was revealed that former Prime Minister Tony Blair had claimed Ŗ10,000 refitting a kitchen in his second home - including a new dishwasher.
Stevenage MP Barbara Follett billed the taxpayer more than Ŗ1,600 for window cleaning at her London home and Liberal Democrat MP Mark Oaten claimed Ŗ245 for a new bed and mattress.
Campaigners say ordinary voters are entitled to know what their representatives in Parliament spend public money on.
They have accused the Commons authorities of "a plot to conceal MPs' expenses".
They claim the exemption is being rushed through, and was deliberately announced on the same day as ministers approved Heathrow's third runway in order to minimise mainstream media publicity.
But they say the internet now offers them a way of by-passing the traditional media by appealing directly to their supporters.
A spokesman for Ms Harman said her opponents "were entitled to their point of view" about the effect of the new rule, and the way in which it was proposed.
However he said Ms Harman would not be responding publicly until Thursday's debate.
Unlock Democracy director Peter Facey said so far protests against the proposed FOI exemption had been largely restricted to what he termed "the civil liberties fraternity".
But he was confident many ordinary voters would join the campaign, thanks to the power of the internet.
Mr Facey added: "I challenge senior MPs and leaders of all political parties to say where they stand and oppose this idea.
"The politicians must realise that by behaving so cynically, they will cause great damage to the reputation of Parliament."
So far there is evidence within Parliament of some limited opposition to the plans.
Lib Dem leader Nick Clegg says he will recommend his MPs vote against the exemption.
But so far neither the Parliamentary Labour Party nor the Conservative Party have stated whether they will support or oppose the FOI exemption.
Downing Street has also been silent - in contrast to the last time an FOI exemption for MPs was proposed, and Gordon Brown let it be known that he did not support it.