The architect of the World Trade Center redevelopment in New York is taking the site's leaseholder to court.
Libeskind and Silverstein have clashed over the plans
Daniel Libeskind filed papers at the state Supreme Court on Wednesday, seeking $850,000 he says he is owed in unpaid fees.
A spokesman for the leaseholder, Larry Silverstein, said Mr Libeskind has been paid "many millions" of dollars and cannot justify his claim for any more.
The two men have been at loggerheads over the final design for the site.
Mr Libeskind's design - a complex of angular towers and a 541-metre (1,776-foot) spire - was chosen in February 2003 following an international competition.
But since then, Mr Silverstein has brought in his own architects, who have substantially changed Mr Libeskind's design plans.
Libeskind's design has been modified
The two sides have been in talks over the past six months, but the court papers said Mr Silverstein had refused to pay Mr Libeskind's company "anything approaching the fair value of the services it rendered".
Mr Silverstein's spokesman, Howard Rubenstein, voiced surprise at the lawsuit.
"It has always been our desire to avoid a senseless courtroom fight," he said.
"That being said, we fully expect to prevail."
News of the legal action comes less than two weeks since Mr Libeskind and Mr Silverstein sat on the same stage amid great fanfare as the cornerstone of the Freedom Tower was laid at Ground Zero.