President Trump signs an executive order while surrounded by small-business leaders in the Oval Office of the White House on Jan. 30. (Andrew Harrer/Bloomberg)

Three advocacy groups filed a sweeping federal lawsuit Wednesday, challenging President Trump’s executive order requiring two federal regulations to be “identified for elimination” for every new one added — arguing that the order fundamentally takes over Congress’s powers to enact laws to protect public health, safety, and the environment.

“The Executive Order exceeds the President’s authority under the Constitution, usurps Congress’s Article I legislative authority, and violates the President’s obligation to ‘take Care that the Laws be faithfully executed,’” says the lawsuit filed by Public Citizen, the Natural Resources Defense Council, and the Communications Workers of America.

The executive order in question did not garner nearly as much attention as Trump’s executive order on immigration. Yet although in a very different sphere from immigration, the question the lawsuit raises is similar to that now playing out in court before the 9th Circuit — does a Trump executive order violate a very basic element of the Constitution?

The executive order requires agencies to compare major regulations based on their costs — it does not take into account their benefits — and for every new one issued across the government, requires that two of roughly equal cost be undone. But the advocacy groups contend that this is arbitrary — why go backward on, say, two vehicle safety standards so that you can institute a new and different one? They add that major laws enacted by Congress and implemented by agencies, such as the Clean Air Act or Endangered Species Act, do not contain any provision instructing that their application should be limited based on cost, or on what other parts of the government are doing.

Within a matter of hours, the case had drawn the White House’s attention. Sean Spicer, Trump’s press secretary, dismissed the lawsuit at a news briefing Wednesday, arguing that the case itself “is wildly inaccurate. It makes a ton of assumptions that call for speculation on what may or may not happen in the future, it’s just subjective at best and doesn’t have any basis in fact.”

Among legal observers, reactions were quite varied.

“The lawsuit charges that the executive order violates the Constitution and federal statutes by replacing existing legal standards with the ‘1 in, 2 out’ standard made up by President Trump,” said Lisa Heinzerling, a professor of environmental law and regulation at Georgetown University Law School. “The president cannot instruct agencies to ignore the legal standards Congress has imposed on them.”

However, far more skepticism came from Jeffrey Holmstead, a former Environmental Protection Agency assistant administrator under George W. Bush who now works at Bracewell LLP on environment and energy law.

“This is a messaging lawsuit,” Holmstead said in a statement. “They have no chance of winning.”

“There is no final agency action, and they don’t have standing because they can’t point to any immediate harm,” he added. “They may well point to the EO in challenging a future Trump rule, but they can’t challenge the EO itself.”

Those will be major difficulties facing the lawsuit, agreed Tom McGarity, a scholar who studies regulation at the University of Texas at Austin law school. But McGarity also said that the groups get at deep issues involving whether the president is indeed required to “take Care that the Laws be faithfully executed,” as the Constitution states. And he said that while this early and ambitious lawsuit may founder, it sets the stage for what is likely to be a string of intense battles over how Trump has moved, with one order, to bring much of the regulatory state grinding to a halt.

“The environmental groups are going at this with all guns blazing,” said McGarity. “It’s a broad argument, it’s by no means a frivolous lawsuit. … I think it’s going to be a hard case to win. It is a kind of a shot across the bow to the administration, that you can write these executive orders, but you’re going to run into resistance when they cause agencies to conflict with what Congress has told them to do.”

The lawsuit was filed before the U.S. District Court for the District of Columbia, and names not only Trump but also Mark Sandy, the acting director of the Office of Management and Budget, which will implement the executive order and has already issued guidance on it. In addition, it names the heads of numerous federal agencies.

In their complaint, the advocacy groups run through multiple major federal laws and some of the regulations they have so far engendered, in areas ranging from occupational health, to vehicle safety, to energy efficiency mandates, to endangered species protections. In each case, the suit poses a similar question: Did Congress really intend that, in order to protect a new endangered species, two others should cease to be protected — or that several other regulations in some different area (such as worker safety, perhaps) should vanish?

“To repeal two regulations for the purpose of adopting one new one, based solely on a directive to impose zero net costs and without any consideration of benefits, is arbitrary, capricious, an abuse of discretion, and not in accordance with law,” the suit contends.

McGarity said that the case against Trump himself may be the hardest to win — the constitutional clause requiring the president to “faithfully execut[e]” the laws has rarely been tested, he said — but when it comes to the Office of Management and Budget, which implements the executive order, that could be another matter. If that office, through the order, requires federal agencies to behave in arbitrary ways that don’t live up to what the laws require of them, then he thinks green groups will have a foothold. The same goes for agencies themselves.

In other words, any way you look at it, the suit could mark the beginning of a major battle over Trump’s attempt to halt regulations that he claims are overly expensive and have harmed businesses.

“I have persuaded my colleague to do an article about this one, we’re just going to follow it, because it’s going to raise a ruckus,” McGarity said.