The GMB union obtained the data under a freedom of information request, which showed public sector workers were paid 0.6% less than those in similar roles in the private sector in 2016.
In 2015 public sector workers were 0.9% better paid than private sector counterparts while in 2010 state employees were 5.8% better paid, according to the Treasury’s figures.
Although, the GMB said, the Treasury did not publish the 2016 data as in previous years and it initially “failed” to release it under a the Freedom of Information Act.
The GMB stated it was not until it officially complained and threatened to refer the Treasury to the Information Commissioners' Office that the figures were released.
Rehana Azam, GMB national secretary for Public Services, said: “This is nothing short of an attempted cover up, but it’s no wonder that ministers fought tooth and nail to cover up these damning figures.
“The Tories can never again claim that public sector workers are ‘overpaid’ when the Treasury’s own assessment proves otherwise.”
She called on the government to use the upcoming Budget to fully fund above-inflation pay rises.
This follows Office for National Statistics figures, which showed inflation hit 3% in September while pay increased for most public sector workers, except prison and police officers, remained capped at 1%.
A Treasury spokesperson rejected the cover up claim from the GMB, stating “There was no delay in releasing the information”.
They said: “Salaries in the public sector are now broadly comparable to those in the private sector after running ahead of the private sector for many years.
“Many public sector workers benefit from generous pension entitlements, giving around a 10% premium in many cases.
“We have confirmed the across-the-board 1% public sector pay policy has been lifted and the independent pay review bodies will report their recommendations in spring 2018.”
Earlier this year the GMB highlighted that one million public sector jobs had been lost since 2010 as funding cuts and outsourcing affected the sector.
