An NHS consultation into the future of Newark hospital is invalid, according to protesters.
NHS Nottinghamshire County wants to replace the accident and emergency unit with a minor injuries unit .
The consultation found a large majority backing the move but campaigners claim too few people took part.
The Campaign to Save Newark Hospital, which organised its own petition, is now calling for every household in the town to be balloted.
The NHS has said patients will get better emergency care if treatment is concentrated in fewer centres.
But opponents believe Newark is being downgraded and people will have to travel further when seriously hurt.
About 2,000 people responded to the NHS consultation, with 700 completing a questionnaire which mainly backed the project.
Campaigners have claimed that is only a fraction of the population, the process was flawed and it broke government guidelines.
The group's chairman Dr Ian Campbell said: "We don't think that people have been given enough time to respond, we don't think they have been given enough information to respond.
"And indeed ultimately we don't think they have been given enough choice about the options."
The NHS Trust has strongly refuted the allegations, saying the process was "robust" with leaflets, meetings and wide publicity.