BAR boss David Richards expects to challenge Jenson Button after the driver's shock defection to Williams for 2005 and 2006, despite having a contract with BAR.
He was able to get out of that deal using a clause that invalidates BAR's hold on him should the team risk losing their works Honda engine supply.
Richards described the clause as a "technicality" and with Honda renewing their supply deal just two weeks ago, he feels BAR have been taken for a ride.
He told BBC Radio 5 Live: "About 36 hours ago we had a letter suggesting that on a very slim technicality that the option wasn't viable based upon Honda's commitment to us. Obviously this is something that is quite ridiculous and we will challenge it.
"You can't go through life taking advantage of legal technicalities - you have to look at the essence of an agreement."
Richards has been unable to speak to Button since discovering his star driver's intention, with the Englishman enjoying Formula One's summer break.
He added: "It's not about contracts, it's about personal relationships. We'll have to speak to Jenson himself and try to discuss it. Basically he's never had one word of criticism and I have numerous emails from his management suggesting that it's a formality he will stay with the team not just next year but the year after.
"I am rather dumbfounded. We are here at the factory with 400 people that I have to brief shortly because people want an explanation. Until we can speak to him personally and find out what's going on with him it would be unfair to criticise him."
Button will team up with Australian driver Mark Webber at Williams next season, with the Grove-based team enjoying a long-term relationship with engine supplier BMW.