General Motors, Fiat Chrysler and Toyota said Monday they were intervening on the side of the Trump administration in an escalating battle with California over fuel economy standards for automobiles. Their decision pits them against leading competitors, including Honda and Ford, who this year reached a deal to follow California's stricter rules. The Trump administration has proposed a major weakening of federal auto emissions standards set during the Obama administration, prompting California to declare that it will go its own course and keep enforcing the earlier, stricter standards. The automakers siding with the administration, led by the industry group the Association of Global Automakers, say that the federal government, not California, has the ultimate authority to set fuel economy standards. The legal fight between the Trump administration and California over auto pollution rules has swelled into a battle over states' rights and climate change that is likely to only be resolved once it reaches the Supreme Court. The Obama-era national fuel economy standard requires automakers to build vehicles that achieve an average fuel economy of 54.5 miles per gallon by 2025, which would eliminate about six billion tons of carbon dioxide pollution over the lifetime of those vehicles. The Trump administration is planning to roll back the fuel-economy standard to about 37 miles per gallon. Nearly two dozen other states have filed suit against the Trump administration, alongside California, over the emissions rules.