Plans to allow roadgoing hypercars to race for outright honours in the 2020/21 World Endurance Championship will be abandoned if no manufacturers make a firm commitment this week.
WEC promoter and Le Mans 24 Hours organiser the Automobile Club de l'Ouest and the FIA, who jointly write the rules for the series, will ask manufacturers to pledge to its hypercar concept category at a technical working group meeting in Paris on Thursday.
The call follows a change to the original philosophy of a class calling for prototypes that looked like hypercars to a twin-pronged approach in which production-based hypercar machinery competes alongside the purpose-built contenders.
That was the result of a meeting between the rulemakers and Aston Martin, Ferrari and McLaren at which the manufacturers expressed concern over the potential costs of the original prototype category.
None of the three has committed to developing a roadgoing hypercar for the WEC at a time when there are no detailed rules for the class.
The move by the FIA and the ACO comes against uncertainty over the future of hypercar prototype projects caused the changes to the rules resulting from the decision to incorporate roadgoing machinery.
Toyota has said that it has started work on a hypercar prototype, though it has yet to make a firm commitment to remain in the WEC beyond 2019/20 and another season with its existing TS050 HYBRID LMP1 car.
Niche manufacturer Glickenhaus and WEC stalwart ByKolles have both stated an intent to compete with a prototype built to the new rules in 2020/21.
It appears unclear if the rule makers will revert to the original hypercar concept rules for prototypes published last December if they do not get the commitments they need on Thursday.
WEC boss Gerard Neveu talked at the Sebring 1000 Miles round in March of a plan B if there weren't sufficient takers for the two-pronged hypercar approach, though without going into detail.
Alternative options for the top class of the WEC appear to include an idea involving uprated GTE machinery.
The concept, dubbed GTE+, appears to have been barely been discussed, if at all, in the technical working group, but there are understood to be manufacturers lobbying for this route in the background.
The ACO is also known to be looking at the North American Daytona Prototype international category.
It sent its international technical delegate, Thierry Bouvet, to the Mid-Ohio round of the IMSA SportsCar Championship on the same weekend as the Spa WEC round earlier this month to attend a rules meeting on the future of the DPi class.
The ACO refused to discuss the 2020/21 rules over the course of the Spa event and promised more news on the future at its traditional press conference in Le Mans week.