East Sussex County Council will object to Brighton and Hove Albion's plans to build a community stadium at Falmer.
Brighton and Hove City Council's support for the scheme was attacked as county councillors voted to object to the project.
Councillor David Neighbour, who represents Falmer, said: "We have a duty to oppose the hypocrisy of the city council, supporting a national park and wanting to railroad this application through before it happens.
"I think it is our duty to protect the area from development and I think we should send a strong representation to Brighton and Hove about where we are coming from."
His comments came as the county council's planning committee agreed unanimously to object to Albion's plans.
The club has submitted two applications to build the 22,000-seat stadium inside the Sussex Downs area of outstanding natural beauty (AONB) at either Village Way North or Village Way South, Falmer.
Both sites are inside Brighton and Hove, with the latter inside proposed boundaries of the South Downs national park.
County councillors were subjected to intense lobbying from both sides before the meeting to decide whether to object.
The council said the stadium had clear economic and social benefits but the environmental impact and associated transport problems could not be overcome.
Councillors were told the Albion had not demonstrated there were no other sites and studies of the alternatives were out-of-date.
However, Coun Rupert Simmons said there were good road and rail links and the difficulties finding a site in overcrowded Brighton and Hove should be recognised.
He said: "There is a need for the stadium and it has to go somewhere. There needs to be an element of sympathy to those strains."
East Sussex County Council joined another neighbouring authority, Lewes District Council, in opposing the scheme.
Eric Huxham, who chairs Falmer Parish Council, said: "We are very pleased with the outcome of Lewes and now East Sussex councils. It just leaves Brighton to follow suit on the planning applications."
Brighton and Hove City Council will decide the two applications at a date to be fixed.
The Green Party has formally objected to Brighton and Hove Albion's two planning applications to build a new stadium at Falmer.
Greens on Brighton and Hove City Council have backed a move to apply for the scheme to be called in for a public inquiry by the Environment Secretary.
They are opposing the scheme on environmental grounds, and convenor Keith Taylor said: "We're not anti-football."
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