Renault could quit Formula One if they are not allowed to develop their engines during the course of next season, Red Bull team principal Christian Horner has warned.
The French manufacturer, partners to Red Bull and sister team Toro Rosso, has been lagging champions Mercedes and Ferrari since the complex new V6 turbo hybrid power units were introduced in 2014.
In-season development, through a complicated system of 'tokens', has been allowed this year but the 2016 regulations in their current form put an end to that unless there is unanimous agreement to relax them.
Horner told reporters at the Canadian Grand Prix that dominant champions Mercedes should think of the bigger picture before resisting change.
"The situation is we are at a precarious point in terms of Renault's commitment to the future," the Briton said.
"If you are effectively shutting that down (the engine development) in February, you are almost waving goodbye to them (Renault).
"So (Mercedes) need to have a bit of a grown-up think about it. And the FIA as well to say what is in the best interests of F1. If F1 can afford to lose an engine manufacturer, then stick to Feb. 28."
Horner said a development freeze would be the worst thing for Renault, who have said they are assessing all their options in the sport.
The manufacturer has a contract with Red Bull through 2016 but has not ruled out quitting or taking a greater involvement in a team.
The sport has only four engine makers, with McLaren's partner Honda struggling even more than Renault and equally keen on constant development.
Red Bull, who won four successive drivers' and constructors' titles until Mercedes swept both last year, have also suggested they could be forced out if they do not have a competitive engine.
"We are looking at a lot of options, including getting out of Formula One," Renault F1 managing director Cyril Abiteboul said in March.
However, he told Reuters last month that the company, who championed the V6 engines before their introduction, had a long-term plan.
"Our plans right now are to stick with what we are. We are an engine supplier and we have to do a better job on the technical side," said the Frenchman. "We have had our difficulties, that's what we need to focus on."