only need a simple majority. >> well, that ends today. >> reporter: republicans are steam-rolling democrats, slashing regulations from the obama era using an obscure law called the congressional review act. >> it has been used once in the past before, but now we're seeing it at least five times this week alone, and we've heard reports that could reach 15 total regulations, maybe even 20 total regulations. >> reporter: this week, republicans repealed regulations preventing mining companies from dumping their waste in local waterways, limiting greenhouse emissions from energy companies, and requiring the social security administration to share medical information with the fbi. the congressional review act allows for a quick rollback on regulations passed in the last six months of the obama presidency with a simple majority vote. >> okay. >> reporter: once the president signs off, the agency cannot re-enact a similar rule, an unprecedented tactic to overturn