Coca-Cola has threatened legal action against a Hampshire restaurant - named Relentless - claiming the steak house's sign breaches its trademark.
The soft drink giant claims the Relentless Steak & Lobster House in Southsea breaches the trademark on its Relentless energy drink.
Owner Scott Matthews, 24, said he was "gobsmacked" at receiving a 17-page legal document demanding it be changed.
He said the restaurant was named after his father's fishing boat.
Mr Matthews said the lettering on the sign had been written in an "Olde English" font on his home computer.
Coca-Cola has given Mr Matthews until 9 November to remove or redesign the restaurant sign, which it says looks too similar to the branding of its energy drink.
Mr Matthews said reprinting the sign would cost £700 to £1,200. But he added he was confident of winning any legal battle over the trademark.
"There are too many differences in it - I don't see how you could get the two confused," he said.
"It's just ridiculous really... we'll fight it all the way."
Coca-Cola confirmed it had contacted the Relentless Steak and Lobster House, which opened in March, and requested that it redesign its current logo.
A company spokesperson said: "We believe it bears a strong resemblance to our Relentless energy drink design and that this may lead to consumers thinking the two are connected.
"In line with our trademark rights, we take action to protect our brands and to avoid consumer confusion."