A coalition of 13 state attorneys general led by New York's Eric Schneiderman has told the Trump administration that it could expect a "vigorous" legal challenge to any attempt to weaken pollution standards for light-duty vehicles.

The Pennsylvania Department of Environmental Protection also signed a letter that the state attorneys sent to Scott Pruitt, the Environmental Protection Agency's administrator. The group said they would oppose any attempt to weaken emissions standards for the model years 2022 to 2025, the group announced.

In March, President Trump promised to reopen a federal review of fuel economy standards that was concluded in the final days of the Obama administration. Automakers had asked Trump to reopen the mid-term review in February.

In their letter, the coalition said it strongly disagrees with Pruitt's contention that the mid-term evaluation process was flawed and provided a point-by-point rebuttal of the administrator's criticisms.