There is uncertainty whether a vote on expenses will go ahead
A frontbench Conservative MP has said it would be wrong if the proposed overhaul of MPs' expenses left members of Parliament worse off.
Shadow Northern Ireland minister Laurence Robertson said the allowances system must be more accountable.
But he said he would not support plans that would make MPs "poorer".
Conservative leader David Cameron says the cost of "doing politics" must be reduced and that is essential to restoring confidence in Parliament.
MPs are due to vote next week on government plans to replace the controversial second homes allowance with a flat-rate daily fee for attending Parliament.
The Conservatives and Lib Dems oppose the plans, saying they are even less transparent than the existing system, and some Labour MPs are believed to have reservations about them.
Mr Robertson said the "clocking in" proposal - which would not require MPs to provide receipts for expenditure - was unworkable as it would effectively allow "MPs to swipe in and then go off and play golf".
An e-mail he sent expressing his concerns about the likely impact of the proposed changes on MPs' financial position was leaked to the London Evening Standard.
In it, he said MPs "should not be bounced into a system...simply because the home secretary claimed less than £10 for a porn film or because another MP employed someone who did very little".
MPs have been under fire over their expenses since it emerged that Tory Derek Conway paid his son for work as a researcher despite him being a full-time student.
Mr Robertson told BBC News the current system of allowances needed to be "cleaned up" and that MPs should be required to account for "every penny" they spend.
But he said this did not mean that MPs should be left worse off.
"If you ask anyone if they would like to be poorer, they would say no," he said.
"If you ask me if I would like to be poorer, I would say no."
The Tewkesbury MP has claimed more than £140,000 in second home allowance - a £24,000 annual payment which covers the cost of MPs having to stay away from their main residence on parliamentary business - in the last seven years.
A series of scandals involving MPs' second-home claims have undermined public confidence in the system and prompted Gordon Brown to call for speedy reforms.
Mr Robertson said he would not defend Mr Conway or anyone else who had abused the system but said it was "unfair" MPs were stigmatised for operating within the rules as they stood.
He said that his MP's salary was his sole source of income and MPs should be compensated for having to work long, anti-social hours and spending long periods away from their families.
If allowances were reduced, without any equivalent rise in MPs' basic pay, members of Parliament would simply seek more work outside Parliament to top up their incomes.
"Do people want their MPs to do more work outside of Parliament? I don't think so."
Cutting expense levels also risked dissuading people from running for Parliament, he added.
If that happened, the only people becoming MPs would either be multimillionaires "out of touch with ordinary people" or "anoraks" who just wanted to become MPs for the sake of it.