Staffordshire Ambulance Service has been engulfed in "a web of deception and lies" over the use of trained volunteer staff, an MP claimed.
In a heated Commons debate, Michael Fabricant (Con Lichfield) accused the chairman and chief executive of Staffordshire Ambulance Trust of misleading the public.
But opposition MPs accused Mr Fabricant of peddling "conspiracy theories" and unfairly attacking ambulance managers.
The trust has told the volunteers, called Community First Responders, that they can no longer administer seven drugs commonly used for pain relief, asthma or treating hart attacks.
It said this would be a temporary measure while it investigated whether it was operating within the law by allowing volunteers to administer the drugs.
But Mr Fabricant said he feared the decision was prompted by Staffordshire Ambulance entering into a partnership with West Midlands Ambulance Service, which will eventually lead to a full merger.
Health Minister Andy Burnham urged the trust to provide "urgent clarification" so that Community First Responders could administer the drugs again.
But the Department of Health would not intervene, he said. "It is a matter for Staffordshire Ambulance NHS Trust."
Speaking in the Commons, Mr Fabricant said: "Why has the new management of the Staffordshire Ambulance Service in the shape of chairman Robert Lake and acting chief executive Geoff Catling removed vital drugs from CFRs and life-saving equipment from both paramedics and trained volunteers?
"We can only speculate. They blame the law, the Government, and the Medicines Act. But this is a lie as I will demonstrate later."
One possible reason was that paramedics working for West Midlands Ambulance, where CFRs were not used, believed they threatened their overtime and job opportunities, he said.