The Environmental Protection Agency is gearing up to significantly tighten air-pollution regulations for the first time under President Trump.

Driving the news: E&E News, citing three sources, is reporting that the agency will announce tighter tailpipe standards for big trucks on Tuesday. An EPA spokesman didn’t respond to E&E News' request for comment.

One level deeper: Tuesday’s announcement is expected to preview an update to rules that set the standards for nitrogen oxides, a pollutant that contributes to smog and poor air quality, E&E News reports. More details:

State and local air agencies petitioned the EPA to tighten these standards for big trucks, including semis, in 2016.

These standards haven’t been updated since 2001.

The big picture: The primary focus of the EPA under Trump has been to unravel a series of significant regulations put in place by then-President Barack Obama. In most cases, the agency is either working to repeal those rules or replace them with far less stringent versions. This rule is likely to be the exception, not the new norm.