SIPTU is calling on the Government to introduce legislation obliging employers to pay the first four weeks of sick pay for their staff.
It follows reports that the Government is considering a proposal to stop paying the first month of benefits to workers who are unable to work because of illness.
It is estimated the move would lead to savings of €150m per year for the Department of Social Protection.
However, there is no legal obligation for an employer to cover sick pay for an employee who is sick for more than three days.
However, employers and the business group ISME have said they will not accept the measure if it is announced in December's Budget.
Their position has been criticised by SIPTU, whose General Secretary Jack O'Connor said the group is always objecting to public policies.
Mr O'Connor said: "If the Government cuts payments, then employers will have to pick up the tab."