Analysis by the party shows patients are routinely waiting more than 18 weeks for treatment.
Rachel Harrison, GMB National Officer, said:
"After ten years of pay cuts and underfunding, morale among NHS staff is at rock bottom.
"The health service faces a crippling recruitment and retention crisis, leading to 75,000 vacancies and huge waits for routine surgery.
"GMB is calling for a restorative 15% increase to make up for a decade of slashed pay under the Conservatives.
"We have no hesitation in recommending members vote to reject the 3% and no hesitation in supporting members if they want to take action."
