GM and Fiat Chrysler have reported that they purchased federal greenhouse gas emissions credits from Tesla, according to filings made to the state of Delaware and viewed by Bloomberg.

Both the US federal government and California offer automaker credits for selling zero-emissions vehicles. Those automakers can then sell those credits to automakers who exceed their pollution restrictions in a sort of cap-and-trade system that imposes extra cost on automakers not improving the fuel efficiency of their fleet.

Tesla has reported sales of its credits for years, but generally the buyers have been kept private. An exception to this occurred in April, when the Financial Times discovered a deal between Fiat Chrysler and Tesla that was reportedly worth hundreds of millions of euros. According to FT, Tesla had allowed Fiat to pool its European fleet with Tesla's in order to meet strict EU average fuel-economy emissions laws.

Given that news, it's not too surprising that Fiat Chrysler is buying US federal fuel-economy credits from Tesla to help it meet stricter and stricter emissions laws in the United States. What is slightly more surprising is that General Motors is reportedly purchasing compliance credits from Tesla, too. GM is Tesla's most mature competitor in electric vehicle sales (the company sold enough Bolt electric vehicles in Q4 2018 to trigger a phase-out of the federal electric vehicle tax credit). But ultimately, GM sells far more internal combustion engines than it does electric vehicles.

According to Bloomberg, GM is not currently in a position where it needs to buy federal emissions compliance credits. But the company is purchasing these credits from Tesla proactively so that it can easily meet tougher future emissions requirements in the US, especially if Democrats regain power in 2020.

The details of the deals between Tesla, GM, and Fiat were not made public, but we know Tesla sold $190 million worth of regulatory credits in Q3 2018. Bloomberg reports that Tesla has raked in nearly $2 billion in compliance credit sales since 2010.

The current administration's Environmental Protection Agency (EPA) has argued that emissions regulations in the US are too strict and too costly for automakers. Although miles-per-gallon numbers increased in 2017, most automakers used credits they banked in pervious years to reach full compliance with greenhouse gas rules.