Cost of publishing '£500 and above' council expenditure prohibitive
Town halls will not be able to afford to publish every spending decision above £500 online, ministers have been warned.
The shake-up - designed to make local councils "think hard" about spending money - is being introduced with no analysis of the extra cost involved, a Labour MP claimed.
Steve McCabe said: "In these cash-strapped times, should we not have a debate on the cost to local authorities of this new government imposition?
"It may be a good thing for everybody to be able to view this information online, but is it joined-up government when local councils, like everyone else, are being asked to make huge cuts?
"I question whether - with 35% of the population of Birmingham not having online access - it is a justifiable extra cost and whether there has been any analysis of what those costs are."
The claim came as the NLGN think-tank warned that town halls face a "tsunami" of cuts that will slash an astonishing 33% from their budgets over four years.
In the chamber, deputy Commons leader, David Heath, ducked the question of just how much it will cost an authority such as Birmingham to publish every spending decision on its website.
However, it appears increasingly likely that Mr Pickles will stop short of imposing a legal requirement on local authorities to publish everything above the £500 threshold.
A letter to councils instead referred to the "expectation that councils will see the benefits for residents and grasp this agenda".
In addition to spending information, councils have also been urged to publish data on senior salaries, councillor allowances and expenses; minutes of meetings and rubbish and recycling rates.
There was no mention of the £500 when Mr Pickles' flagship Decentralisation and Localism Bill was listed in the Queen's Speech. The Bill itself has yet to be published.
Mr McCabe spoke out as communities secretary, Eric Pickles, pledged to match the pressure on councils, by opening up his own department's spending to the public's gaze.
Speaking to the LGA conference, Mr Pickles said: "I'm embarrassed to look you in the eye and ask you to put all spending over £500 online if my own department is only putting spending over £25,000 online.
"So the Department for Communities and Local Government and its agencies will be putting all spending over £500 online too. I want to lead from the front."
The Tories have compared the impact of their drive for town hall transparency to the push for council meetings to be held in public - pursued, in the 1950s, by none other than Margaret Thatcher.
The party first floated £25,000 as a threshold for councils, but that figure was dramatically lowered after some Conservative councils experimented with a cut-off at just £500.