English Heritage believes visitors to the ruins of the abbey that William the Conqueror built to atone for those who died in battle should be able to buy a cup of tea.
But the Battlefield Trust thinks the proposal is philistine.
Spokesman Michael Raynor says the building - which would include toilets - would lower the dignity of the battlefield.
"I think it's in very questionable taste and extremely insensitive to build such things," he said.
'Think again'
The Battlefield Trust's main objection is that the building would set a dangerous precedent, which could be followed by other developers seeking to build on battlefield sites.
"As the custodian of battlefields, English Heritage should set a standard. When it's as important a battlefield as Hastings, there really shouldn't be any new building close to the centre of it," said Mr Raynor.
The local district council was to have decided on the issue on Thursday - but at the last minute it emerged that English Heritage asked for the application to be deferred.
Mr Raynor says he hopes the English Heritage will think again about its proposals.
The Battle of Hastings was won by the William, Duke of Normandy, and marks the last time England was invaded by a foreign power.
The battle was not actually fought at Hastings, but at the place that became known as Battle, six miles inland.
Northern Ireland
Scotland
Wales
England
English Heritage - Battle of Hastings
Battle of Hastings - Camelot International
1066 - Battle of Hastings
The BBC is not responsible for the content of external internet sites.
Next steps for peace
Blairs' surprise over baby
Bowled over by Lord's
Beef row 'compromise' under fire
Hamilton 'would sell mother'
Industry misses new trains target
Quins fightback shocks Cardiff
(From Sport)
Vodafone takeover battle heats up
(From Business)
IRA ceasefire challenge rejected
Thousands celebrate Asian culture
Christie could get two-year ban
(From Sport)
Colleagues remember Compo
(From Entertainment)
Mother pleads for baby's return
Toys withdrawn in E.coli health scare
Nurses role set to expand
(From Health)
Israeli PM's plane in accident
More lottery cash for grassroots
Pro-lifers plan shock launch
Double killer gets life
Cold 'cure' comes one step closer
(From Health)
Straw on trial over jury reform
(From UK Politics)
Tatchell calls for rights probe into Mugabe
Ex-spy stays out in the cold
Blair warns Livingstone
(From UK Politics)
Smear equipment `misses cancers'
(From Health)
Boyzone star gets in Christmas spirit
(From Entertainment)
Fake bubbly warning
Murder jury hears dead girl's diary
Germ warfare fiasco revealed
(From UK Politics)
Blair babe triggers tabloid frenzy
Tourists shot by mistake
A new look for News Online