Calls for the number of ministers to be reduced in line with a future cut in the size of the House of Commons have been rejected by MPs.
They discussed the issue while debating a political reform bill that would cut MPs' numbers from 650 to 600 by 2015.
Tory MP Charles Walker said the number of ministers must fall in proportion with this or it would appear they were "immune" from austerity measures.
The government said there was time to reconsider this in the future.
The coalition wants to reduce the size of the Commons after the next election as part of efforts to "cut the cost of politics" in response to public anger over last year's Westminster expenses scandal.
In a proposed amendment to the Parliamentary Voting System and Constituencies Bill, Mr Walker said that if the Commons shrunk in size to 600, it was right that there should be a similar drop in ministerial numbers.
He said his "modest" proposal - which would see eight fewer government posts - was in keeping with the general belt-tightening expected of all institutions in the current tough economic climate.
"We live in an age of austerity, things are changing. We are dismissing senior permanent secretaries from across the Civil Service, we are removing chief executives of councils and their directors, we are attacking senior and middle management across the country," he told MPs.
"And yet there is one group of senior management that is completely immune from these cuts and that is the ministerial corps.
"Yes, we are all in it together, but not quite if you are a minister."
Backing the measure, fellow Tory MP Bernard Jenkin - chairman of the Public Administration Select Committee - said it would merely "maintain the status quo" in regard of the size of the government payroll.
Deputy Leader of the House of Commons David Heath said there was "no simple arithmetic relationship" between the number of MPs in the Parliament and the number of ministers as their overall number was "based on need".
While the coalition was committed to handing power from the executive to the legislature, and the number of ministers may be reduced in future, he did not believe this was the "right time" for such a step as the boundary changes assumed by the bill would not come into force until 2015.
"We do need to reduce the scope of government patronage and that is something we are already engaged in," he added.
The rebel amendment was defeated by 293 votes to 241.