Porsche, Audi and Formula 1 are reportedly getting nervous that the Volkswagen Group's plans to enter the sport in 2026 may be thwarted.
Behind the scenes, pressure is building on the FIA to finally announce the detail of the next set of all-new engine rules, which have already been badly delayed.
Liberty Media-owned Formula One Management is pushing for a vote on the regulations in the last days of July, after which both Audi and Porsche will have 15 days to lodge their 2026 entries.
Mercedes boss Toto Wolff, however, wonders why there is such a rush.
"It is not possible to make such a decision dependent on the regulations because they are constantly changing in our business," he is quoted as saying by Auto Motor und Sport.
"We can expect a decision from the new entrants, especially since we have made great strides towards them."
It now emerges that Mercedes, Ferrari and Renault are demanding new limits on engine bench testing - which F1 managing director Ross Brawn suspects is blatant delay-tactics.
"If there is a cost cap, you don't have to worry about the number of test bench hours," he said. "If you invest more money there, you have to save elsewhere."
The existing engine manufacturers also reportedly want the material for engine pistons to be enshrined in the regulations as steel, with Porsche and Audi reportedly pushing for aluminium.
Mattia Binotto denies that Ferrari and its current rivals are simply trying to make life as difficult as possible for the VW brands.
"I think we need to clarify," said the Ferrari boss. "We are very positive about Audi and Porsche joining F1 and I think we've done whatever we could to make sure they are happy.
"We removed the MGU-H and we did it only to try to help them to join F1, even if removing it is something that for us is maybe not the best choice."
Binotto insists that the regulations delay is simply because "they are not ready yet".
"There are still open points and those open points simply need to be tackled and discussed and agreed," said the Italian.
