Campaigners seeking to safeguard the future of maternity services at Causeway Hospital hope to challenge the legality of the facility's proposed closure.
The Northern Trust outlined its options for scaling back services at the Coleraine hospital in February.
The trust said there was less demand for maternity services at the hospital and that it expects birth rates in the area to fall by 11 per cent over the next 20 years.
The Northern Trust wants to build a new £150 million women and children's unit at the site of Antrim Area Hospital.
At a campaigners' meeting in Kilrea, Co Derry last week it was agreed to seek legal advice on the closure of maternity services at Causeway Hospital in the absence of a Stormont health minister.
Campaign spokesperson Gemma Brolly accused the trust of "steamrolling" over people's concerns in what she termed a "cart before the horse approach".
"We have decided to seek legal advice to ascertain whether the management of the hospital or the civil service have the legal authority to close this vital service in the absence of a minister for health," she said.
"In the event their authority to make this decision is legally in question we will seek to pursue legal action against the civil service to save the service."
A petition calling for an "immediate halt to the planned closure of Causeway maternity services" has so far received more than 1,150 signatures.
Mrs Brolly said "all hospital services are interlinked" as she voiced concern for the future of the intensive care unit at Causeway Hospital.
"If this is closed it would put massive pressure on the surrounding hospitals that are already under severe pressure," she said.
"This is the most important health infrastructure in our region and our campaign will fight tooth and nail for its protection."
The Northern Trust has been asked for comment.
