Once again, Texas is suing the federal Environmental Projection Agency­.

Attorney General Ken Paxton on Wednesday filed a lawsuit over the agency’s rejection of parts of a Texas clean air program, launching the state’s second battle against EPA regulations in less than two weeks.

Texas has sued the agency 21 times since President Obama took office in 2009.

This challenge centers on how Texas handles pollution that spews from industrial plants during facility startups, shutdowns and equipment malfunctions.

Historically, regulators exempt pollution from those events from overall limits, letting plants emit more than their federal permits allow. But environmental groups have protested this policy, claiming it has let plants discharge millions of extra pounds of dangerous air pollutants each year.

A federal appeals court in April 2014 found some of the environmental groups' points valid, prompting the EPA in May to require Texas and 35 other states to revisit how they deal with such events.

The new state plans are due in November 2016.

But Paxton said that because the EPA had approved Texas' plans in 2010, before the environmental challenge, the agency's latest directive amounted to “an abrupt and unwarranted about-face.”

“The EPA’s actions make it impossible for even the most carefully-regulated facilities to avoid costly penalties due to unplanned events out of their control,” he said in a statement Wednesday. “We will continue to fight back the EPA’s ongoing efforts to encroach on Texas’ effective management of our air quality standards.”

The lawsuit comes nine days after Paxton joined Louisiana and Mississippi in a battle against the agency’s “Waters of the U.S.” rule, finalized last month. The EPA says those regulations aim to better define the scope of bodies of water protected under the Clean Water Act.

Yet another lawsuit could be coming soon. Paxton has already said he plans to fight EPA’s “Clean Power Plan,” a sweeping plan to combat climate change by slashing carbon emissions from power plants. The agency plans to finalize those rules next month.