The Supreme Court hears oral argument Tuesday in a case that will determine whether a 2018 law gave prisoners a chance to reduce unfairly long sentences for possessing the smallest amounts of crack cocaine.

The bipartisan group of senators who championed the law have told the justices in a brief that they aimed to give everyone sentenced for crack cocaine possession under an old tough-on-drugs law a chance to get their sentence reduced.

That provision was central to the passage of the broader 2018 sentencing overhaul meant to make the criminal justice system more fair and reduce prison overcrowding. It was a signature bipartisan legislative accomplishment during the divisive partisan atmosphere of the Trump administration.

Some federal courts have interpreted the law that way. However, four federal appeals courts have ruled that the 2018 law was written in a way that means it applies to defendants who had larger amounts of crack cocaine but doesn’t apply to those who had the smallest amounts.

The lawyers for the defendant in the Supreme Court case, Tarahrick Terry, told the justices that “countless” low-level crack offenders are still serving their sentences, but “geography alone now determines whether they are even eligible for relief.”

Terry pleaded guilty to possessing 3.9 grams of crack in Florida in 2008 and was sentenced to more than 15 years in prison under the Anti-Drug Abuse Act of 1986, which had three levels of penalties based on how much crack cocaine was possessed. That law had a now-infamous disparity that treated crack 100 times more severely than powder cocaine, which meant Black and Latino defendants disproportionately received harsher sentences.

Congress has changed the sentencing laws twice since then. First, in a 2010 law known as the Fair Sentencing Act, lawmakers changed the threshold for how much crack cocaine defendants had to have possessed before they qualified for a higher level and stiffer sentences. But that law applied only to new defendants, not for Terry and others who had been sentenced already.

Then Congress passed the 2018 law known as the First Step Act, which sought to make the 2010 law retroactive. That would mean those sentenced for crack cocaine possession under the 1986 law now could ask a judge to reduce their sentences.

That provision was key to the passage of the broader 2018 law, because a House bill without the provision could not get enough support in the Senate, a bipartisan group of senators told the justices in a brief in the case.

And outside groups such as the American Civil Liberties Union conditioned their support on such provisions, according to the brief from Senate Judiciary Committee Chairman Richard J. Durbin of Illinois, Iowa Republican Sen. Charles E. Grassley, New Jersey Democratic Sen. Cory Booker and Utah Republican Sen. Mike Lee.

“Across the political spectrum, the Act’s supporters stressed that the retroactivity provision was necessary to achieve the Act’s purpose — to make it, in the words of Senator [Richard] Blumenthal, a true ‘first step toward a fairer, more humane system,’” the lawmaker brief states.

But the Justice Department under the Trump administration argued in cases across the country that the law as written does not apply to Terry and those sentenced under the lowest of the three levels.

The 2018 law says that “covered offenses” are those that were modified by the 2010 law, and the Justice Department says that the 2010 law changed the threshold only for the two higher levels.

Two federal appeals courts, based in Boston and Richmond, Va., have ruled that district court judges have discretion under the 2018 law to reconsider the sentences for the lowest-level crack offenders. In one ruling, for example, the court decided that changing the threshold that would move a defendant from the lowest level to the middle level — which was 5 grams under the 1986 law and 28 grams under the 2010 law — means that it modified the lowest level as well as the middle level.

That has led to reductions in sentences for pre-2010 crack possession an average of 71 months, or 26 percent, with more than 90 percent of those Black defendants, the lawyers for Terry told the Supreme Court.

But federal appeals courts based in Atlanta, Philadelphia, Denver and Cincinnati have ruled the opposite way and said judges can’t reconsider those sentences, including the U.S. Court of Appeals for the 11th Circuit in Terry’s case now before the Supreme Court.

The Trump administration defended the 11th Circuit’s ruling back in December. But the Biden administration notified the Supreme Court that it would no longer defend that position and believes Terry’s conviction is a “covered offense.” Now, the justices have appointed a third-party “amicus” to defend the lower court’s ruling at oral argument.

Durbin and the other senators argue in their brief in the case that the 11th Circuit faulted Congress for not making “an unnecessary textual change” to the lowest-level offense, “for not legislating surplusage, contrary to the basic tenets of statutory interpretation.”

“Had Congress intended to exclude individuals with low-level crack offenses from relief, Congress of course could have done so,” the senators wrote.

Tuesday’s arguments are the last of the current session, and a decision in the case is expected by the end of the term in late June.