An environmental group today abandoned its legal challenge to one of the Obama administration's greenhouse gas rules, which it had claimed did not go far enough in regulating industry.

The Center for Biological Diversity filed a petition last year taking aim at U.S. EPA's "tailoring" rule, which requires large facilities to limit their greenhouse emissions (Greenwire, Aug. 2, 2010).

Industry groups and some states also challenged the rule, wanting it struck down altogether, but CBD was the only petitioner saying the rules were not strict enough.

CBD was scheduled to file its opening brief in the case on June 20 but instead filed a motion to dismiss today.

The overall case will still proceed, focusing solely on the other challengers. Their briefs are also due June 20.

The tailoring rule is one of four climate rules facing legal scrutiny before the U.S. Circuit Court of Appeals for the District of Columbia (Greenwire, March 23).

Legal experts say it is the most vulnerable of the rules because EPA was essentially forced to rewrite part of the Clean Air Act in order to avoid requiring small polluters -- like farms and schools -- to obtain permits.

CBD attorney Kassie Siegel said today that, as EPA continues to roll out its greenhouse gas permitting program, including a new phase due to start next month, "it just became unnecessary to litigate these particular claims."

On July 1, EPA is set to extend the permitting requirements to new construction projects that emit at least 100,000 tons of greenhouse gases and existing facilities that increase their emissions by at least 75,000 tons per year, even if they do not exceed thresholds for other pollutants (Greenwire, May 13, 2010).

Sources that emit at least 100,000 tons of greenhouse gases per year will also be required to account for greenhouse gas emissions in their operating permits.

The CBD petition "was about ensuring that EPA moves forward as quickly as possible," Siegel said.

One lawyer, who declined to be named because he is involved in the case, speculated that CBD withdrew its petition because its attorneys "realized that the tailoring rule is probably the best thing they're going to get out of EPA on greenhouse gases, and that the rule is in real danger of being struck down."

CBD wouldn't want anything "it would have said attacking the rule from the other side to undermine the rule," the lawyer added.

Click here to read the motion to dismiss.

Reporter Gabriel Nelson contributed.