Hundreds of NHS workers will stage a second one-day strike next week, to coincide with the Labour Party conference, in a protest over the privatisation of services, union officials said today.

Workers at NHS Logistics, who deliver the likes of bedpans, gloves and food to hospitals and GPs' surgeries across England, voted in favour of industrial action last week, in protest at the transfer of their jobs to German-owned delivery giant DHL.

They are already set to strike for 24 hours on Thursday, the most significant industrial action in the NHS for nearly 20 years.

Today, the trade union Unison announced that a second strike would take place on September 26, when the Labour conference is scheduled to debate the health service.

"The NHS will be a hot topic at this year's Labour Party conference and Unison's contemporary motion highlights the outsourcing of NHS Logistics to DHL," said Karen Jennings, the union's head of health.

"Taking strike action on the very day that health is to be debated by the Labour conference will put our members' protest centre-stage.

"They have worked hard to build NHS Logistics into an award-winning service and don't deserve to be treated in this way. There is simply no logical explanation for this transfer."

Unison says workers will draw up emergency plans, but warn that the strike could see hospitals run short of some items.