LMP1 manufacturers will be permitted to race only three distinct aerodynamic configurations in next year's World Endurance Championship and then only two from 2017.
The introduction of the limit follows the escalation of aero development by Porsche and Audi through 2015, during which they each raced at least three different bodywork specifications.
The new rule came out of the budget-reduction working group on which the P1 manufacturers sit and was agreed at last week's FIA World Motor Sport Council, although the final wording of the regulation has yet to be worked out.
Toyota Motorsport GmbH technical director Pascal Vasselon told Autosport: "In 2014, Audi and us were using two packages, but this year I think Porsche maybe even had four.
"The idea is to progressively cut back to return to the situation we were in before."
The rule will cover major body items, such as wheel arches and engine covers, but there will be freedom in terms of what Vasselon called "cheaper items" such as vanes and dive planes.
Porsche LMP1 technical boss Alex Hitzinger stated that it was also important to "allow freedoms in order to balance the cars for different tracks".
Hitzinger added that the rule would not result in significant budget savings next year, but would when the lower limit comes into force in 2017.
"The rule has really been devised to avoid real excesses in terms of aero development," he explained.
The new rule will go hand in hand with restrictions on the hours each manufacturer can spend in the windtunnel over the course of a calendar year.
This will be set at 1200 hours next year, with a reduction to 800 hours planned for 2017.
The WEC rulemakers - Le Mans 24 Hours organiser the Automobile Club de l'Ouest and the FIA - and the manufacturers have opted against following the lead of Formula 1 by also setting limitations on the use of computational fluid dynamics (CFD).
"It is not really possible to police and it is less relevant to cost reduction," said Vasselon.
Hitzinger said that Porsche was happy to agree to the limitations: "All we want is a level playing field and then it is up to us to do a better job."
Audi is known to have opposed limits on windtunnel time for 2015 and is understood to have maintained that position going into the latest talks.
The limit of 50 car-days of testing introduced for 2015 will, as scheduled, be reduced for next season.
It will go down to 43 days, with 40 days planned for 2017.