Red Bull have launched a protest against the legality of Mercedes' car at the Austrian F1 Grand Prix.
It relates to a device on the steering wheel that allows the drivers to alter the tyre angle when in a straight line.
Red Bull have questioned if the system is actually an aerodynamic aid, rather than for steering and a decision is expected in the next 24 hours.
"Obviously we're keen just to get clarity on that system using the mechanisms that are available and getting it addressed quickly early in the weekend," Red Bull chief Christian Horner told Sky Sports before making the protest.
"We have a difference of opinion on the system. Its primary performance isn't to steer car obviously so, yes, of course there is a technical position that Mercedes will think one thing, our engineers think something else so in situations like this the best thing is to address it via a protest.
"It depends what it actually does and achieves," Horner added. "Everything has to earn its place on the car.
"Obviously it's a clever system, it's an ingenious system but obviously these rules are so complex. It's just understanding what part of the regulations it fits."