Cornish nationalists have called on the mayor of Truro to pull out of a celebration of the patron saint of England, St George.
The Loving Cup tradition has medieval origins, say organisers
The Celtic League says the event on 12 March is insensitive to Cornish people who will be celebrating the adopted patron saint of Cornwall, St Piran.
A week of St Piran's events clashes with the "Loving Cup" celebration.
Loving Cup organisers Celebrate St George's Day said the aim was to bring people from communities together.
Mike Chappell of the Celtic League said in a letter to Truro City Council: "Cornwall has its own patron saint in the form of Piran and does not need to adopt the English patron Saint George by being part of the Loving Cup tour."
He told BBC News Online: "A lot of people do not identify with the flag of St George.
"They identify with the flag of St Piran, which is a sign of Cornish distinctiveness.
"It is completely inappropriate and offensive being so close to St Piran's Day."
This the first year that Celebrate St George's Day has organised the Loving Cup event, which it says is based on a tradition going back to medieval banquets symbolising "trust and friendship".
Fifty cities are taking part in the "Grand Tour of the Loving Cup" which started in Norwich on 5 February and ends in Westminster on St George's Day: 23 April.
Bruno Peek, of Celebrate St George's Day, said: "The whole aim of the loving cup is to be inclusive, not exclusive.
"It is not about being English. It is a simple, gentle way to bring people together and no-one has refused so far."
St Piran's celebrations start in Cornwall on 5 March
He said the timing of the event was not planned to coincide with the St Piran events.
He added: "My message to the objectors is grow up and live in the real world.
"I am looking forward to my visit to Cornwall."
A spokesman for Truro City Council said the event was going ahead as planned.
He said: "We very much support St Piran, and always have done.
"There are Cornish pasties sold in Covent Garden and the captain of the England rugby team is Cornish. I think the two can live together."