The highest court in Massachusetts is hearing arguments in a case that could determine the fate of thousands of people convicted of drug crimes based on tainted evidence.

The American Civil Liberties Union says many of those affected are afraid to vacate their guilty plea and seek a new trial because they can be prosecuted for crimes dropped when they entered their plea deal.

The ACLU will argue Thursday morning that the Massachusetts Supreme Judicial Court should declare that any defendant who seeks a new trial cannot be convicted of a more serious offense or given a longer sentence.

The case comes after former state drug lab chemist Annie Dookhan admitted she faked test results and tampered with evidence.

Dookhan was sentenced to at least three years in prison in 2013.