Thousands of workers will be hit by the changes, which will strip between $172 and $225 a week from the pockets of full-time contract cleaners who work in government buildings.

The changes are among the 9500 regulations to go under Prime Minister Tony Abbott's red tape ''repeal day'' on Wednesday.

Buried in more than 50,000 pages of regulations and acts of parliaments to be scrapped is the revelation the government will abolish the Commonwealth Cleaning Services Guidelines for cleaners employed on government contracts from July 1.

The regulations are a form of collective bargaining introduced by Labor that lift the wages of workers hired by businesses that win government cleaning contracts, by between $4.53 and $5.93 an hour above the minimum wage. This brings their weekly wage from $664 to $836 for a 38-hour week for level 1, and from $724 to $950 a week for level 3 workers.

United Voice, the union representing cleaners, would not comment on the changes before consulting its members. It is understood the union was not aware of the changes and is trying to negotiate with contractors and the government in an attempt to mitigate the effects on its members.

Labor introduced the Cleaning Services Guidelines in 2011 to tackle the exploitation of vulnerable workers in the contract cleaning industry. A 2010 Fair Work Ombudsman audit of cleaning contractors found that 40 per cent of audited businesses did not comply with workplace laws. It recovered almost $500,000 for 934 underpaid workers.

But with those changes being scrapped, cleaners working on government jobs will again be paid at the award rate.

The Department of Employment says the changes will remove the different rates of pay for workers employed in private and government work.

''Cleaning services providers tendering for government work from July 1, 2014, will still be required to comply with all relevant workplace laws and the modern awards set by the Fair Work Commission,'' it said.

But Opposition Leader Bill Shorten dubbed the change a ''stinker''.

''Tony Abbott's version of red tape reduction is to cut the pay of some of Australia's lowest paid workers,'' Mr Shorten said. ''I don't understand why the Prime Minister is happy to pocket a pay rise every year but is forcing the person cleaning his office to take a pay cut.''

A spokesman for Employment Minister Eric Abetz said: ''There are very strong legal protections and safeguards for workers in the industry contained in the Fair Work Act 2009 and the modern awards system.

''The Fair Work Ombudsman continues to be the government regulator that ensures workers are receiving their correct legal entitlements.''