On Wednesday, Republicans in Congress will get started dismantling President Barack Obama’s environmental legacy — deploying a rarely used tactic to overturn two big federal regulations around coal mining and methane leaks (as well as three other rules).

The background here is that it would be tricky and time-consuming for the Trump administration to repeal many Obama-era regulations all by itself. But Congress can easily wipe out a subset of Obama’s agency rules using the 1996 Congressional Review Act, which allows the House and Senate to nullify any recently finalized federal regulation by a simple majority vote in both chambers — so long as the president agrees.

What counts as “recently finalized” here gets complicated, but Congress can basically use the CRA to repeal any rule finished by Obama after mid-June 2016 — a list that spans more than 50 major regulations. This week, the GOP will focus on killing two big environmental rules plus three others:

The stream protection rule for coal mining. This regulation, finalized in December 2016, would sharply restrict coal-mining companies from dumping debris and waste into nearby waterways in the future. Also, before starting a new mine, coal companies would have to develop a plan and set aside money to restore affected streams once finished. Advocates say the rule is crucial to protect fragile ecosystems and limit the dumping of toxic heavy metals into water supplies. But the coal industry — which is already in sharp decline — says it would put large swaths of the nation’s untapped coal reserves off-limits and further crunch mining companies. The methane waste rule. This Department of Interior regulation, finalized in November 2016, would require oil and gas companies to reduce methane leaks from operations on federal and tribal lands. Instead of just flaring it or letting it waft into the air, companies would have to capture the methane and sell it off. This rule was a component of Obama’s climate plan, which aimed to reduce emissions of methane — a powerful greenhouse-gas — from oil and gas drilling 40 percent by 2025. But the oil industry preferred this be regulated at the state level (which is typically looser). The “resource extraction rule.” This SEC regulation, finalized in June 2016, would require publicly traded oil, gas, and mining companies to disclose payments they make to foreign governments. It was done under the auspices of the 2010 Dodd-Frank financial reform bill. Its supporters say the increased transparency would deter corruption from oil companies working abroad. But oil companies hate it — when Trump’s new Secretary of State Rex Tillerson was head of ExxonMobil, he flew to DC to lobby against it, arguing it would put US energy companies at a competitive disadvantage. The “blacklisting” rule for contractors. This rule, finalized by the Department of Labor in August 2016, would require federal contractors to disclose labor law violations from the last three years — and change their practices — before they can receive a contract. In October, a federal judge halted this rule from taking effect, saying it went beyond the authority Congress had given the executive branch. The Social Security gun rule. Under this regulation, finalized in December 2016, the Social Security Administration would submit information on recipients of disability insurance to the National Instant Criminal Background Check System if they met certain “mental impairment” criteria. Gun-rights advocates said the system could block those on disability from being able to buy guns and rallied to repeal it.

The House is voting vote to repeal all these rules on Wednesday and will then hand things off to the Senate. Trump is expected to approve all these moves.

The CRA has only been used successfully once before — in 2001, the congressional GOP and George W. Bush used it to rescind a Clinton-era ergonomics rule. Since presidents don’t usually want to gut their own regulations, it’s really only useful to attack last-minute rules finished by a previous president, assuming there’s unified party control.

To make things more complicated, the CRA also says that once a rule’s been killed, federal agencies can’t ever come back and issue a new rule that’s “substantially the same form.” But that provision has never really been tested — what counts as substantially the same? — and it’s unclear how this might be adjudicated.

The five rules targeted this week may just be the beginning. Republicans could conceivably use the CRA to strike down a flurry of other final-year Obama regulations in the weeks ahead (these fuel-economy standards for trucks might be one target) Democrats don’t have the votes to stop them, and CRA votes are immune from a Senate filibuster. The only real hurdle here is how much time the GOP actually wants to spend mucking around with CRA votes, as opposed to moving on to other business, like health care or taxes.

Further reading: If Trump wants to dismantle Obama’s regulations, here are the obstacles he’ll face