Businessman Jimmy Cairns has applied for a licence to sell shellfish from an old-fashioned cart on the picturesque promenade.
But he has come under fierce opposition – as it could jeopardise one of the town's most prominent family businesses.
Starr Butchers in High Street, which also sells fresh fish, said it may have to lay off staff if Mr Cairns is given the go-ahead.
Michael Starr has owned the shop for 19 years and says he is already struggling.
'I have to pay wages and rates for 12 months a year while he will pay a tenth of that and soak up all the summer trade,' the 64-year-old said.
'There is no doubt that I will have to let the girl who works on the fish counter go because I can't compete with that.
'And that means Emsworth will be left with no fishmonger in the winter.
'I don't want to make someone unemployed but I'll have no choice.
'If he was opening up a shop I would accept that because we'd be on a level playing field but he isn't.'
Two of the three Emsworth ward councillors support the plans and a petition put before Havant Borough Council has 324 signatures in support of Mr Cairns.
But Brendan Gibb-Gray, Emsworth councillor and chairman of the Emsworth Business Association, is opposing the application.
He said: 'Whilst I'm an advocate of competition, I like competition to be fair.
'It does sound like a good idea and if we didn't have a fish shop already I would agree, but we have.
'Do we just want someone who is active for a few months or do we want someone who sells a wide range throughout the year?
'I've spoken to a lot of people who think it is a really good idea but fish is a precarious thing to sell and it could mean someone at Starr's loses their job.'
Havant's licensing committee will meet next Wednesday to discuss the issue.
Mr Cairns was not available for comment.