Campaigners fighting to save A & E services in Huddersfield have asked experts for help.
They have drafted a letter to the Independent Reconfiguration Panel outlining concerns about the proposals.
The Panel is a body which reviews proposals for changes to NHS services and advise the Secretary of State for Health.
It has intervened in several controversial hospital plans in the past.
They look at plans relating to hospital-based services, community-based services or specialised regional or national services with a focus on patients and quality of care.
Natalie Ratcliffe, secretary of the #handsoffHRI campaign group, has written to the Panel requesting their advice regarding the current proposed changes to local NHS provisions.
The plans would see emergency services switched from the Royal Infirmary to Calderdale Royal Hospital, with the Infirmary being replaced with a smaller hospital.
She said: “So far our Campaign is a group of over 47,000 concerned citizens.
“The proposed changes from Greater Huddersfield CCG and Calderedale CCG have led to a debate in Westminster Hall with Ben Gummer, organised by our local MPs Jason McCartney and Barry Sheerman et al.
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“We have also gathered 62,000 signatures with an online petition and at the current count we have over 25,000 signatures on a similar paper petition. We have organised two rallies to demonstrate local dissatisfaction with these proposals, the latest one gathered between 8,000 and 10,000 people.
“We have organised several more fundraising events and are in the process of arranging several public meetings to further discuss the proposal.”
The Hands Off HRI Campaign is also in discussion with legal teams to look at the available options.
Martin Houghton, the IRP secretary, said: “The IRP is aware of developments in Calderdale and Huddersfield having previously been contacted by a local representative in the area. I believe that 14 week formal consultation has begun this week on proposals for changes to services.
“Whilst the Panel is willing to offer informal advice to any parties requesting it, it is important to allow the formal consultation to proceed so that all views can be heard and considered.
“Any advice offered by the Panel at this stage would necessarily need to be generic in nature so as not to interfere with that process.”