Sir Frank Williams insists Jenson Button will join his Formula One team next season despite the driver's insistence he will stay at BAR.
Button, 25, says a contract he signed with Williams for 2006 is not binding.
But Williams said: "We have a fully binding contract. There's no let up. It's clear to understand.
"Once you give your word you need to keep your word. Jenson is emphatically not for sale. We are a serious racing team and we need him."
Williams insisted there would be "absolutely no turning back" with the driver who first entered the sport with the team in 2000.
But Button wants to stay at BAR because he believes they offer him the best chance of an elusive first Grand Prix win.
Williams said he understood his concerns but that he was willing to fight the Englishman in the courts should he pursue legal action.
The Grove-based team have contractual obligations with their sponsors which rest on Button returning to them.
"We have a proper and correct legal right," he said. "We require him to be here, our sponsors are predicated on his presence - we have promised."
He also attempted to allay Button's fears over Williams' potential for success in 2006. The Grove-based team are tipped to sign a one-year engine deal with Cosworth for 2006 after current supplier BMW bought the Sauber team.
"We are well resourced - as well resourced as any team in the paddock," he said.
"We will be back and Jenson is part of our equipment to do that. It will be nice to have a British driver in a British team.
"I hear and understand his concerns about his present team's competitive position and our uncompetitive situation.
"We shall be back, if not in the second half of this year then certainly next season."
Williams says he wants to talk to Button in the two-week gap after the Hungarian Grand Prix to clarify his point of view.
He added: "We need an opportunity to explain to Jenson where we are today on our road map back to the top of the grid, and where we will be tomorrow."