McLaren are pressing ahead with legal action against Red Bull Racing after the latter signed head of aero Dan Fallows.
Earlier this month Red Bull announced that Fallows, who had previously left the team to join McLaren, would be returning as their head of aerodynamics.
Almost immediately McLaren disputed the appointment.
McLaren racing director Eric Boullier stated: "Dan Fallows has a legally binding contract with McLaren and the matter is now in the hands of our lawyers."
And those lawyers are now pressing ahead with High Court action.
According to McLaren group chief executive Ron Dennis, Fallows signed a legally-binding contract with the Woking team only to pull a U-turn and head to Red Bull.
"To be honest that's completely unacceptable to us," Dennis told Autosport.
"Just days before Fallows' McLaren start date - and despite having signed a legally-binding contract with McLaren, being on gardening leave from Red Bull, and moving to a new home near Woking - he suddenly informed us that he no longer wanted to work for us.
"The problem was, he had no legal basis on which to make that U-turn because he'd already formally accepted, and contracted himself to, our offer of employment."
He added: "Sadly, it's now likely that McLaren will have no alternative other than to pursue a High Court action against Red Bull, which will ask very serious questions as to that team's integrity and sense of fair play."
The Brit also claimed that McLaren's attempts to contact Fallows prior to the Red Bull announcement had been "met with stony silence."