More than 400 executives said that the decision ignored both scientific and legal precedent and that, if the ruling stood, it would create uncertainty for the pharmaceutical and biotech industries.The pharmaceutical industry plunged into a legal showdown over the abortion pill mifepristone on Monday, issuing a scorching condemnation of a ruling by a federal judge that invalidated the Food and Drug Administration’s approval of the drug and calling for the decision to be reversed.The statement was signed by more than 400 leaders of some of the drug and biotech industry’s most prominent investment firms and companies, none of which make mifepristone, the first pill in the two-drug medication abortion regimen. It shows that the reach of this case stretches far beyond abortion. Unlike Roe v. Wade and other past landmark abortion lawsuits, this one could challenge the foundation of the regulatory system for all medicines in the United States.“If courts can overturn drug approvals without regard for science or evidence, or for the complexity required to fully vet the safety and efficacy of new drugs, any medicine is at risk for the same outcome as mifepristone,” said the statement.Also on Monday, the Justice Department filed a motion asking the U.S. Court of Appeals for the Fifth Circuit to stay the ruling by Judge Matthew J. Kacsmaryk of the U.S. District Court for the Northern District of Texas until the department’s appeal of the case could be heard. Judge Kacsmaryk, a Trump appointee who has written critically of Roe v. Wade, had issued only a seven-day stay of his ruling to allow the government a chance to appeal.“If allowed to take effect, the court’s order would thwart F.D.A.’s scientific judgment and severely harm women, particularly those for whom mifepristone is a medical or practical necessity,” said the Justice Department motion, which noted that mifepristone was also used in treating miscarriages. It added: “This harm would be felt throughout the country, given that mifepristone has lawful uses in every state. The order would undermine health care systems and the reliance interests of businesses and medical providers.”The appeals court gave the plaintiffs, a coalition of groups and doctors who oppose abortion, until midnight Tuesday to file a response.A lawyer for the plaintiffs, Erin Hawley, said in a statement on Monday, “Chemical abortion drugs don’t provide a therapeutic benefit — they can cause serious and life-threatening complications to the mother, in addition to ending a baby’s life.”She added that “the F.D.A. put women in harm’s way, and the agency should be held accountable for its reckless actions.”The Justice Department also filed a motion in a separate lawsuit over mifepristone. That case, filed in Washington State against the F.D.A. by 18 Democratic attorneys general who challenged extra restrictions that the agency imposes on the drug, produced a contradictory order less than an hour after the Texas ruling, which was issued on Friday evening.Judge Thomas O. Rice, an Obama appointee, did not lift the extra restrictions but told the F.D.A. not to do anything to limit current access to mifepristone in the jurisdictions that had filed the suit, which represent a majority of the states where abortion remains legal.In its motion in that case, the Justice Department said there was “significant tension” between the Texas and Washington rulings and asked Judge Rice to clarify what the F.D.A. would be obligated to do if the Texas ruling took effect — essentially seeking instructions from the judge that would allow the agency to continue to keep mifepristone available.The dueling rulings by two federal judges have set up a legal showdown that is likely to end up in the Supreme Court.”This is absolutely a test of our legal system’s ability to function,” Phil Weiser, the attorney general of Colorado, said in an interview. Colorado is a plaintiff in the Washington case and one of nearly two dozen states that signed briefs supporting the F.D.A. in the Texas case before both the district court and, on Monday, before the appellate court.Mr. Weiser said that the Texas decision violated “basic principles” about “how you make judgments based on evidence and about the authority of agencies.” He added, “The challenge is, once you start undermining those rules in one case, you undermine it for others as well.”The larger destabilizing potential of the Texas ruling was at the root of the letter signed by the biotech and pharmaceutical executives.Dr. Jeremy Levin, the chief executive of Ovid Therapeutics and the former chairman of BIO, a biotech trade association, said in an interview that he and a few other industry leaders had been worried about the Texas lawsuit since it was first filed in November. “It completely upends the F.D.A.’s authority,” Dr. Levin said of Judge Kacsmaryk’s ruling. “And then, much more importantly, it opens it up to a political determination of what a medicine is or isn’t, and that is deeply harmful for vaccines, Alzheimer’s drugs, all the others.” Dr. Shehnaaz Suliman, the chief executive of ReCode Therapeutics, said that she and Dr. Amanda Banks, the former chief executive of Blackfynn Therapeutics, began drafting the letter a few weeks ago, after a March 15 hearing in the case in Judge Kacsmaryk’s courtroom in Amarillo, Tex.“The primary message is the concern about the court’s overreach and how it might apply to other disease areas or products regulated by the F.D.A.,” said Dr. Suliman, who was involved in organizing a “call to action” among members of the industry in response to the Supreme Court’s decision last year to overturn Roe v. Wade.“The F.D.A.’s evaluation of safety and effectiveness for products is the gold standard in the world,” she said, “and our industry relies on this to foster the kind of innovation that has resulted in drugs that have saved millions.” On Friday evening, after the ruling was issued, Dr. Suliman and Dr. Banks shared their draft with Dr. Levin and three other executives, meeting with them virtually to fine-tune it. Then, Dr. Banks and others “pulled an all-nighter,” Dr. Levin said, working Friday night through Saturday to complete it.The group emailed the draft to about 100 leaders in the industry, many of whom signed and also circulated it to their employees and other industry executives, Dr. Levin said. Asked whether anyone declined to sign, he said, “In our experience, people don’t decline — they just don’t respond.”Most of the signatories are not involved in reproductive health. One signatory, Pfizer, makes a small percentage of the U.S. supply of the second drug in the medication abortion regimen, misoprostol, which is approved for other medical conditions but used off-label for abortion. A spokeswoman for Pfizer said that the company did not support off-label use of any of its medicines, but that the F.D.A. “serves a critical role in the U.S. public health system — bringing new medicines to patients and conducting ongoing safety reviews that support the continued use of them — that must be maintained.”Legal scholars said the Texas ruling appeared to be the first time a court had tried to invalidate the approval of a drug over the objection of the F.D.A. For decades, Congress has given the agency authority to determine whether drugs are safe and effective.The ruling could be so far-reaching for pharmaceutical companies that the letter from industry leaders is probably just the beginning of the industry’s actions to oppose it, said Jennifer Oliva, a professor of law at the University of California College of the Law, San Francisco, who signed a brief submitted to Judge Kacsmaryk’s court by drug policy scholars in support of the F.D.A.“They’re going to heavily lobby state legislatures, Congress and get involved in the courts in these battles going forward because it threatens their livelihood,” Ms. Oliva said.