Justice Samuel Alito said the plaintiffs argued in court filings that studies have shown after the 2021 change from the FDA that allowed mifepristone to be mailed that there was an increase in emergency room visits.

He asked Solicitor General Elizabeth Prelogar if the FDA's response -- that there were not increases in side effects from the drug -- was proper.

Preolgar said this was a reasoned explanation from the FDA and the agency acknowledged that while some studies have shown the availability of abortion pills by mail led to more ER visits, this did not equate to "more serious adverse effects."

"Many might go because they are experiencing heavy bleeding which mimics a miscarriage and they need to know whether or not they are having a complication," she said.

Being cited in the arguments is the Comstock Act, a 151-year-old law under which it's illegal to use carriers such as the United States Postal Service to mail "obscene" materials such as drugs that induce abortions.

The Alliance for Hippocratic Medicine has said the FDA's decision to allow patients to receive mifepristone by mail instead of in person from certified health providers specifically violates the Comstock Act.

Solicitor General Elizabeth Prelogar, pressed by Justice Samuel Alito on why the FDA didn't consider the application of the Comstock provisions, said she did not think it fell under the FDA's "lane."

"And we don't think it means what respondents suggested," Prelogar said of the law.

Read more about the Comstock Act here.

Amid questions from the Supreme Court about who has standing to sue, Solicitor General Elizabeth Prelogar said the federal government believes individual doctors still have broad "conscience protections" if they oppose abortion and decline to provide such access in specific instances.

Prelogar reaffirmed that later in the hearing when some justices returned to the topic but noted that the government believes there are exceptions under the law.

Preolgar previously argued that the government does not believe states have standing in this case to sue.

Solicitor General Elizabeth Prelogar is arguing the supposed harm cited by the anti-abortion alliance is "unduly speculative" and hypothetical.

"Their theories rest on a long chain of remote contingencies," she said. "Only an exceptionally small number of women suffer the kind of serious complications that could trigger any need for emergency treatment. It's speculative that any of those woman would seek care from the two specific doctors who asserted conscience injuries."

Prelogar also asserted that if there were any safety consequences to a drug, the FDA could take action itself to fix it.

With the hearing wrapped, after about two hours of arguments, the Supreme Court appeared highly skeptical of the challenge to the mifepristone regulations brought by a group of anti-abortion doctors -- suggesting recent steps to ease access to the medication used by millions of American women may be allowed to stand.

At the heart of the case are steps taken by the FDA in 2016 and 2021 to roll back safety measures around the pill, which was first approved for use in 2000.

The plaintiff doctors -- who do not prescribe mifepristone, use mifepristone or otherwise perform abortions -- claim that wider availability of the drug was authorized improperly and has adversely impacted them, forcing them to care for women in emergency rooms suffering complications from the pill, often in violation of their conscience.

While conservative-leaning Justices Samuel Alito and Clarence Thomas were the most sympathetic to the legal challenges, for the most part, the court on Tuesday steered clear of openly second-guessing FDA’s scientific analysis of mifepristone.

A majority of the justices, across the ideological spectrum, expressed doubt during the arguments that the doctors had sufficiently demonstrated legal standing that they had been directly harmed by the FDA’s mifepristone rule changes.

“It makes sense for individual doctors to seek a [conscience] exemption but they already have that,” said liberal-leaning Justice Ketanji Brown Jackson. “What they are asking for here is -- in order to prevent them from ever having to do these kinds of procedures -- that everyone else should be prevented from getting access to that medication. How is that not overbroad?”

That view was echoed by conservative-leaning Justice Neil Gorsuch.

Erin Hawley, the attorney for the doctors, was repeatedly pressed to provide specific examples or testimony from a physician who had been forced to violate his or her conscience in treating a mifepristone patient but she could not do so.

Solicitor General Elizabeth Prelogar, defending the FDA on behalf of the Biden administration, warned of "profound harm" for women and for drug companies working with the FDA should the lower court's restrictions on mifepristone remain.

-ABC News' Lalee Ibssa and Devin Dwyer