In the most closely watched abortion rights case to come before the supreme court in nearly two decades, the eight high court justices on Wednesday spent an intense hour sparring over the fate of what many consider the strictest abortion law in the nation.

The case concerns House Bill 2, an abortion restriction passed in Texas in 2013 that many regard as the toughest in the nation. The legislature justified the law as a necessary health measure, although major medical groups such as the American Medical Association have questioned whether it actually makes abortion any safer.

Looming over the proceedings was the absence of Justice Antonin Scalia, who would have almost certainly voted to uphold the law. After his death, it is likely that the justices will, at most, reach a tie on the outcome, which would limit but not blunt the dramatic impact of a ruling that upholds the Texas law.

US supreme court takes on biggest abortion rights case in two decades Read more

The court’s four liberal justices seemed distinctly on the side of the providers. In a dramatic moment of the arguments, Scott Keller, the solicitor general for the state of Texas, struggled to answer their barrage of questions about the need for such a law in Texas. Justice Elena Kagan, conceding that the court allowed states to single out abortion providers, asked: “Why would Texas do that?”

A hard-to-read Kennedy was silent for long stretches of oral arguments. Both sides regard him as a crucial ally in the final decision. Early in the arguments, he asked if it would be useful to remand the case back to the lower court, to explore how many abortions a reduced number of clinics could provide.

The bill is the most hotly contested abortion restriction in the country, and the first in the wave of hundreds of recent abortion regulations to be aired before the supreme court. The outcome of the case could have broad implications for abortion access and the anti-abortion movement across the US. A district judge struck down the law on the basis that there was little medical evidence to justify the burden it placed on Texas women. A three-judge panel drawn from the fifth circuit court of appeals, the most conservative in the nation, later reversed that decision, causing abortion rights providers to appeal in Washington.

A portion of the bill requiring providers to have admitting privileges – the ability to admit and treat patients – at a hospital no more than 30 miles away closed nearly half of 41 clinics. Another prong, requiring abortion facilities to meet the same, expensive standards as hospitals, is not in effect but threatens to close all but nine clinics.

Or so a group of Texas abortion providers challenging the law has argued. On Wednesday, the conservative members of the court grilled Stephanie Toti, the attorney from the Center for Reproductive Rights representing the providers, on the extent of the evidence that the law would force clinics to close.

Justice Samuel Alito questioned whether there was direct evidence that 11 clinic closures the day the admitting privileges became required were actually linked to HB2. He also expressed skepticism that the law actually closed nine Texas clinics that ceased providing abortions shortly before the admitting privileges rule.

Chief Justice John Roberts noted that Planned Parenthood, which operates five of the nine clinics in Texas that meet the hospital-like requirements, was not party to the lawsuit – proof, he suggested, that it is not difficult to comply with the law.

But the most pointed questions were those that four liberal members of the court reserved for Keller.

Justice Stephen Breyer pressed the Texas solicitor to describe the nature of the problem with abortion that Texas was trying to correct.

“Where in the record will I find evidence of women who had complications and could not get to a hospital?” asked Justice Stephen Breyer. “Which were the women? On what page does it tell me their names and their complications?”

Facebook Twitter Pinterest Pro-choice advocates rally outside of the supreme court as the justices hear oral arguments in the Whole Woman’s Health v Hellerstedt case. Photograph: Drew Angerer/Getty Images

Keller responded that the supreme court in previous cases had permitted lawmakers to hold abortion facilities to heightened health standards.

“According to you, the slightest health improvement is enough to burden hundreds of thousands of women,” said Justice Sonia Sotomayor. “Is that your point? … Can the legislature say anything?”

Justice Ruth Bader Ginsburg asked Keller how many Texas women would live more than 100 miles from an abortion clinic if the law were fully in place. When Keller noted that El Paso women in the far west corner of the state could drive one mile over the border to a clinic in New Mexico, Ginsburg pounced.

Texas is defunding Planned Parenthood clinics. What if every state did? Read more

Why count clinics in New Mexico, she asked, when New Mexico does not hold its clinics to the same supposedly high standards as abortion clinics in Texas?

The stakes in this case are especially high because the supreme court has never explicitly spelled out how far states can go in restricting abortion ostensibly to protect women’s health. The court has said that states can make laws to protect women’s health as long as they do not constitute an “undue burden”. But it has never clarified what constitutes an “undue burden”, or whether a law is an undue burden if it does not serve an actual health purpose. The latter is a question that has divided the lower courts.

Donald Verrilli, the US solicitor, seemed mindful of those facts as he told the court, “I think the question before you is whether the right here”, the right to an abortion, exists only on paper or “still retains its substance”.

The justices, in their questions for Toti and Keller, sparred with one another over various points of fact.

Ginsburg, with an air of incredulousness, asked why Texas felt the need to require women to complete medical abortions – first-trimester abortions induced with pills – in what amounts to a mini-hospital.

When Kelly responded that medical abortions were still prone to complications, Ginsburg further noted that complications were most likely to occur after the woman has gone home. The law requires providers to have connections within 30 miles of the clinic. “30 miles of what?” Ginsburg said.

Roberts noted that three ambulatory surgical centers, the term for outpatient surgery facilities that meet the strict standards set by HB2, had opened up since the law’s passage. One of those, a Planned Parenthood clinic in Houston, was able to perform 9,000 abortions a year.

To say that nine clinics could provide abortions for the entire state, he said, “does not stretch credulity”.

Verrilli clarified that between 65,000 and 70,000 abortions were performed annually in Texas prior to the law, and the ASCs open today can provide only 14,000.

He noted that the cost of converting an existing clinic to an ASC starts at $1.6m and a new ASC can start at $3.5m. Toti later added that the three clinics to have opened since the law passed were in the works for years.

Clarence Thomas shocks supreme court by ending 10-year oral argument silence Read more

Besides Texas, seven other states – Alabama, Kansas, Oklahoma, Louisiana, Mississippi, Wisconsin and Tennessee – have passed similar abortion restrictions that have been contested in federal court. Those laws collectively threaten to shut down dozens of abortion clinics across the south and midwest, and their fates are tied to the outcome of Wednesday’s arguments: a broad ruling against the Texas law would probably have the effect of striking down all those laws.

An expansive ruling in favor of Texas would have allowed all those laws to take effect, devastating the number of abortion clinics across the south. But this scenario is less likely than it was a month ago. The death of Scalia has all but erased the possibility that a five-justice majority will vote to uphold Texas’s law.

But the remaining justices could tie in a 4-4 split. A tie sets no precedent – leaving the questions presented to the court unanswered – and it allows the ruling on appeal to go into effect. In this case, that means the Texas law would take effect.

Justice Clarence Thomas refrained from asking any questions – his custom, although on Monday he surprised the legal world by breaking his silence from the bench for the first time in a decade.

Scalia’s chair was empty and draped in black.