Public sector employers have been urged to give sick pay to all their workers after a new study found it was not being paid to some cleaning and catering staff in schools and hospitals.
Unison said it was "angry and frustrated" after discovering that many contracted-out catering and cleaning workers in schools and hospitals were denied sick pay, even if they were on the minimum wage.
General secretary Dave Prentis said: "It cannot be right that these massive multinational companies can make huge profits but still cheat workers out of basic terms like sick pay - it is enough to make anyone sick."
He continued: "Cleaners and dinner ladies in schools and hospitals are paid on or just above the minimum wage, and struggle to make ends meet. Many also struggle into work when they are sick, risking their own health and the health of people around them. This is particularly true in hospitals where vulnerable patients may be put at risk by catching infections."
Unison said it was "outraged" at recently announced Government plans to scrap the two-tier workforce code in the public sector, warning that more workers' rights could be "sacrificed" for company profits this year.
"We want local authorities, hospitals and contractors to do the right thing and make a New Year resolution to pay all their staff sick pay. They must ward against this 19th century-style treatment, and make 2011 the year for fair treatment," said Mr Prentis.
Under the current two-tier workforce code, new starters employed by contract companies are meant to get broadly comparable wages, terms and conditions as staff transferred across from the public sector.
The code was developed to prevent private contractors making savings by driving down staff terms and conditions.
Unison said it feared scrapping the code will lead to services being sold to the lowest bidder, leading to increasing numbers of workers suffering cuts to terms and conditions, with sick pay at the top of the hit list.
The union claimed that firms with contracts to provide catering and cleaning services in schools in Reading and Westminster and hospitals in Buckinghamshire, Birmingham and East Kent were among those not giving sick pay.