WASHINGTON (AP) — A unanimous Supreme Court is speeding up the time for generic biotech drugs to become available to the public in a ruling that means a loss of billions in sales to the makers of original versions.

The justices ruled Monday in favor of generic drug maker Sandoz in its dispute with rival Amgen over a near-copy of Amgen’s cancer drug Neupogen.

The case involves biologics — drugs made from living cells instead of chemicals. The drugs have led to major advances in treating diseases, but come at steep prices.

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A 2010 law allows cheaper generic versions known as biosimilars to be produced after a 12-year exclusive run for the original.

Writing for the court, Justice Clarence Thomas said the law does not require companies making biosimilars to wait an extra six months after gaining Food and Drug Administration approval before selling the drugs.

The extra time can add billions of dollars in additional sales to the original drug makers before biosimilars enter the market.

The dispute involves the drug Zarxio, a generic that Sandoz developed to compete with Neupogen that sells for about 15 percent less than the original product. The drugs help boost red blood cells in cancer patients.

California-based Amgen filed a patent infringement lawsuit claiming that Sandoz violated the 2010 Biologics Price Competition and Innovation Act. That law requires biosimilar makers to give a six-month notice of sales to rivals.

A federal appeals court sided with Amgen in 2015, ruling that the notice can’t take place until after biosimilar makers gain approval from federal regulators.

Sandoz, a unit of Swiss drug giant Novartis, argued that the appeals court had it wrong and was unfairly giving an additional six months of exclusive sales to the original drugmaker.