The FIA will only allow Formula 1 teams to run Dual Axis Steering (DAS) systems until the end of 2020, with the device having been already outlawed from the start of 2021.
The main talking point of pre-season testing so far has been the steering idea, which alters the toe angle of the front wheel through the steering wheel being pushed backwards and forwards.
Mercedes has checked with the FIA about the legality of DAS, and the governing body's view is that it is allowed because the device only alters the steering angle of the front wheels.
While rival teams are now considering whether to copy the idea themselves, or challenge it by arguing that the toe-angle illegally changes the front suspension, it has emerged that the FIA has already moved to outlaw teams from running anything like it in 2021.
F1's 2021 regulations, which were published at the end of last year, are clear that any changes to the angle of the steered wheel can only be made by the steering wheel rotating in a defined way.
A new Article 10.5 of F1's Technical Regulations states: "The re-alignment of the steered wheels, as defined by the position of the inboard attachment of the relevant suspensions members that remain a fixed distance from each other, must be uniquely defined by a monotonic function of the rotational position of a single steering wheel."
Sources have confirmed that the interpretation of that regulations means that DAS, and systems similar to it, will not be allowed.
It is unclear if the addition to the rules for 2021 was part of a normal process to clear up certain areas of the current rules, or was prompted as the direct result of the FIA being alerted about Mercedes' plans several months ago.
The one-year grace period for DAS comes following recent comments from F1 that such lengthy freedom for radical design ideas will not happen longer term.
Earlier this month, F1 managing director of motorsport Ross Brawn said that future governance would allow quick responses to shut down ideas that had clearly exploited rules loopholes.
"If one team stands out there with a solution that had never been conceived and had never been imagined, and destroys the whole principle of what's trying to be done, the governance would allow, with sufficient support from the other teams, to stop it. And this is a whole different philosophy," he said.
"And what then happens, someone who has a loophole thinks to themselves, do I want to use it and risk it being stopped? Or do I want to tell the FIA about it because it wasn't intended?"