Farm and biofuel groups, as well as Iowa lawmakers, ex­pressed disappointment over last week’s decision by the U.S. Supreme Count overturning a lower court ruling that severely restricted petroleum refiners’ ability to use waivers to skirt rules of the Renewable Fuel Standard (RFS).

But the biofuel advocates noted that limits on the waivers, called Small Refinery Exemptions or SREs, remain intact after Supreme Court ruling. In addition, they urged the Biden...