Originally Published: 14 JUN 21 10:30 ET

Updated: 14 JUN 21 11:43 ET

By Ariane de Vogue, CNN Supreme Court Reporter

(CNN) -- The Supreme Court held Monday that a low-level crack-cocaine offender is ineligible to seek a reduced sentence under the Trump-era First Step Act sentencing reform law.

The vote was 9-0.

At issue in the case is whether low-level crack-cocaine offenders who were convicted before Congress changed sentencing guidelines in 2010 are eligible for lower sentences under a sentencing reform law passed in 2018.

Under federal law there is a three-tier sentencing structure for cocaine offenses. Tiers "1" and "2" concern convictions for large and medium amounts of cocaine, while Tier "3" is reserved for low-level offenders. In 2010 Congress increased the amount of crack quantities required for the two higher tiers out of concern for disparities between sentences for powder and crack cocaine and allegations that the sentences reflected race-based differences. In 2018, lawmakers passed the landmark, bipartisan First Step Act, making changes retroactive for crimes committed before 2010.

The case at hand involved Tarahrick Terry, who was convicted in 2008 with possession with intent to distribute 3.9 grams of crack cocaine. He was sentenced to 188 months in prison under Tier "3." Terry is set to complete his term of imprisonment on September 22, 2021, and then will begin serving six years of supervised release. His lawyers, supported by the Biden administration, said he should be eligible for a reduced sentence under the statutory changes.

A lower court ruled, however, that Terry's offense did not merit a reduced sentence because the law did not target low-level offenders. It only changed the quantity guidelines for Tiers "1" and "2."

Writing for the unanimous court, Justice Clarence Thomas said that Terry's offense was "starkly different" from those that triggered mandatory minimums.

Justice Sonia Sotomayor agreed with the court's interpretation of the law. But, she said, that while the First Step Act "brought us a long way toward eradicating the vestiges of the 100-to-1 crack to powder disparity, some people have been left behind."

She noted that if Terry had been sentenced under provisions of the law that require larger quantities of drugs, he would have been eligible for resentencing under the First Step Act "even if sentenced as a career offender."

As things stand, she said, "Terry never had the chance to ask for a sentence that reflects today's understanding of the lesser severity of his crime."

"Absent action from the political branches," she said, "he never will." She noted that "Congress has numerous tools to right this injustice."

Lower courts have split on whether the change applies only to high and mid-level offenders and not low-level offenders.

Under then-President Donald Trump, the Justice Department defended the lower court opinion, but after the election, the Biden administration reversed course and said Terry would be eligible for a reduced sentence.

Because of the change, the Supreme Court appointed a lawyer to defend the lower court opinion.

The lawyer, Adam K. Mortara, told the justices that when Congress passed the 2018 law it altered the quantity of drugs in each tier, but did not change the penalties.

But Eric J. Feigin, the deputy solicitor general, said that Congress acted to "erase" the taint of disproportionate sentencing.

The case produced a bevy of odd bedfellows who argued in support of the Terry, including the progressive American Civil Liberties Union and the conservative group Americans for Prosperity Foundation.

"Draconian sentencing schemes untethered to the four traditional rationales for punishment -- retribution, incapacitation, rehabilitation, and deterrence -- lead to cruel, unjust penalties for individual defendants, harm their families, damage communities, and undermine the legitimacy of our criminal justice system, all at taxpayer expense," Michael Pepson, of Americans for Prosperity Foundation, told the justices in court papers.

This story has been updated with additional details Monday.