Over half of NHS Direct staff could be made redundant by the end of the year, health union Unison has warned.
According to the union, NHS Direct will close 24 of its 30 call centres and reduce its workforce by half from 1,500 to 750, making nurses and other health care professionals redundant.
Unison described the move as "disastrous", adding that it was "shocked" by the scale of cuts.
The news leaked as Dr Éoin Clarke, founder of Labour Think Tank 'Labour Left', said that the chairman of NHS Direct informed staff of the decision via an internal email explaining the process and timing of the cuts.
The message read: "We do know that the overall number of jobs in NHS Direct will be substantially lower than it is currently - most probably less than half the current number."
Sandra Maxwell, UNISON convenor at NHS Direct, said that NHS professionals who were due to be made redundant could be utilised for the new NHS 111 service "if only the Department of Health took some decisive action".
Michael Walker, UNISON National Officer for NHS Direct, said that Health Secretary Jeremy Hunt should "step in and stop this disaster immediately."
"Axing dedicated hard working nurses is never a good idea at any time, but this will directly impact on patient care. There is no doubt that patients will suffer as a result of this move," he added.
NHS Direct has not confirmed that any of it sites will close.