The Senate on Thursday approved an effort to overturn an Environmental Protection Agency rule tied to the Clean Air Act and designed to limit 7 of the most hazardous air pollutants that are emitted by heavy industry.

The 52-46 party-line vote marked the first time in the 55-year history of the Clean Air Act that Congress has moved to weaken the power of the landmark environmental law.

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The rule tied to the Clean Air Act was finalized last year to close a loophole that required all “major” sources of seven hazardous air pollutants to reduce their emissions by the maximum achievable amount, a policy called “Once in, Always In.”

The rule requires that industrial facilities — often chemical plants, oil refineries, and other industrial factories classified as “major” sources of toxic air pollution — always maintain strict pollution controls. Even if they comply and limit those pollution levels, those facilities would always be labeled “major” sources under the rule.