The Queen Street car park has been earmarked for temporary classrooms for the Bohunt academy, being built in Broadwater Road, Worthing.
But the facility is used as a vital overspill for packed surrounding roads, parking for community groups and the Queen Street Church.
Lead petitioner Catherine Bourner, of Queen Street, said: “It’s going to be awful. The 70 cars which park in the car park every day are not going to fit on the street.
“It’s going to affect the whole of Broadwater, as everyone will be trying to find a parking space.”
The petition was first launched in November after residents learned the car park was being recommended for disposal by Worthing Borough Council, the landowners.
Residents persuaded the council to retain the car park but the new Bohunt school soon presented a fresh problem.
With building works on the school not due to be completed until 2016 – and students set to move in from September – the car park was highlighted as a potential location for temporary classrooms.
The issue is set to be discussed at Worthing and Adur councils’ joint strategic committee meeting, at the Adur Civic Centre, Shoreham, on Tuesday.
Gaisford ward councillor Kevin Jenkins said a solution needed to be found which worked for both students and the community.
He said: “In an ideal world we would not want to have seen temporary classrooms on the car park but we have got to be realistic.
“I think there is a moral obligation for the council to be sympathetic towards the request but at the same time ensure that use of the car park still recognises the needs of the immediate community.” Mrs Bourner said she remained sceptical that any sharing of the car park would leave sufficient spaces for residents, considering the current usage.
The committee will consider whether to grant a lease to West Sussex County Council or Bohunt for the temporary use of the site and a planning application must then be submitted, before any final decision is made.
An alternative temporary site of Palatine Park was explored but disregarded as unsuitable by Bohunt.
Bohunt chief executive Neil Strowger said: “Negotiations suggest that we are moving towards a position that works for both the community and outstanding educational provision.”