Mercedes boss Toto Wolff says that rival team Red Bull approached around 100 of their engineers at Brackley and Brixworth with offers designed to 'poach' key staff.
Wolff said it was inevitable that Red Bull would try and recruit staff from Mercedes, as the team takes over the development of its power unit from Honda at the end of the season.
"It's pretty obvious that if you want to set up an engine factory in the UK, there's only one [place to recruit staff] - and that's us," he told Sky Sports F1 in Barcelona on Friday afternoon.
"The project is a Mount Everest to climb.
"I think they approached 100 people or so and they got 15 maybe," he said. "We have 900 or so employees, and if you're fishing out 15 of these that's pretty normal.
"But they went mainly after manufacturing staff, so it's not really performance. I guess they want to build up the the company."
Red Bull consultant Dr Helmut Marko previously suggested that Mercedes has offered to double the salaries of key engineering personnel who choose to stay at Mercedes.
But Wolff feared that in that case, Red Bull would then offer three times the amount.
"Doubling the salaries is one thing, he said. "But if you triple them, at a certain stage you're not going to compete anymore, even for loyal people."
However Wolff said he understood Red Bull's strategy and didn't hold it against them.
"I'd like to have a fight with Red Bull power units," he insisted. "It is what it is. I respect everybody that wants to defend his business or build their business. And retaliation time has not yet come!"