Red Bull were accused of breaking the rules by McLaren
Formula 1's governing body has warned that any system used to adjust a car's suspension and ride height between qualifying and races would be illegal.
The FIA says they contravene Articles 34.5 and 3.15 of the F1 regulations.
They would give cars that qualified with a light fuel load an advantage by giving them sufficient ground clearance when the tank was filled for the race.
The move comes after McLaren accused Red Bull of having a ride-height device, which Red Bull strongly denied.
Red Bull boss Christian Horner said at the Malaysian Grand Prix that he could "absolutely guarantee" his cars did not use such a system, adding they would protest if any team did use one.
The FIA said on Wednesday: "Any system, device or procedure, the purpose and/or the effect of which is to change the set up of the suspension whilst the car is under parc ferme conditions, will be deemed to contravene Article 34.5 of the F1 Sporting Regulations."
The letter added that the FIA believed "any self levelling damper system is likely to contravene (article) 3.15 of the technical regulations".
Article 3.15 refers to aerodynamics while Article 34.5 states that a driver must start the race from the pit lane if any changes are made to the suspension of his car while it is held under parc ferme.
Parc ferme refers to the period after qualifying and before a race when the cars are effectively off-limits to mechanics.
McLaren team principal Martin Whitmarsh said at the Australian Grand Prix that he believes Red Bull's pace-setting form this season is being aided by a system that breaks Formula 1's rules.
Whitmarsh, speaking well before the FIA's statement was released, added that his engineers were racing to develop a system of their own and hoped to have it ready by next week's race in China.
"Frankly a few months ago if the engineers had come to me and said: 'We're going to design this system,' I would have said: 'Actually, I don't think it's permissible'," said Whitmarsh.
"There's some evidence that perhaps such systems are considered legal and if they are then we're going to get one as quick as we can."
Active ride systems, pioneered by the original Lotus team and then used to great effect by Williams, have been banned under regulations since 1993.