The ballot included nursing assistants as well as support staff such as caterers, ancillary staff and administrators.
The union is now calling an immediate meeting with health secretary Alan Johnson to call for a rethink.
A spokesperson for the GMB said: ‘I have never seen a pay offer turned down by this amount. The three year deal is dead in the water.’
Sharon Holder, GMB National Officer added: ‘The ballot result is a resounding no. This result vindicates the position of the GMB negotiators who knew instinctively that GMB members would not tolerate this unacceptable, long term pay offer. The Department of Health must be instructed to put a one year deal on the table that GMB members can accept.’