Campaigners trying to halt part of a £100m Anglesey waterfront development need to raise £15,000 to fund a legal challenge, a meeting has been told.
They want Newry Beach in Holyhead given protected status, blocking part of the 500-berth marina scheme.
Anglesey council gave the project planning permission in 2012.
But after legal advice, the authority announced a public inquiry would take place in October.
The hearing will examine whether parts of Newry Beach should be given village green status, under laws designed to prevent building on valued community spaces.
Developers have insisted the plans would see "enhancement of Newry Beach", including improved public access and facilities.
However, campaigners fighting the plans under the Newry Beach Holyhead Action Group banner said it would lead to a "concrete curtain" on the waterfront.
"We have got to the point where we have got to have more help," chairman of the group Prof Terry Looker told a meeting of about 150 people in the town on Thursday evening.
"It is now or never."
He told the audience at Holyhead High School the campaigners needed about £15,000 to appoint a barrister to lead their legal case within the next two or three weeks.
The meeting heard about half of the money is in place either through being raised or pledges.
But the issue has split views in Holyhead, with the town council continuing to back the plans, which developers said would create 700 jobs.
A spokesman for the authority said "it must remain neutral as far as the merits of the village green application are concerned".
Conygar-Stenaline declined to comment on the hearing, which is due to start on 3 October and will last up to a week.
The Holyhead Waterfront scheme is being put forward by developers Conygar and the ferry and port operator Stenaline.
In addition to the marina, the proposals would cover a 34 hectare site, stretching from the Great Breakwater to Newry Beach, encompassing Porth-y-Felin.
It would include:
- 500-berth marina
- A mix of 326 apartments and houses
- 80-bed hotel
- Youth centre
- Public beach area with changing facilities
- A new maritime museum and visitor centre
- Car parking