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.

The Republican-led Congress appears ready to approve the Keystone XL oil pipeline, but no matter what actions are taken in Washington, the entire 1,179-mile project could be delayed until Nebraska signs off on the route.

After several years of intense debate, the routing process is before the Nebraska Supreme Court, and depending on how the justices rule, months or years could pass before construction begins in that state.

Even if approval comes from Washington and the high court, opponents are looking for new ways to block the project, including filing a federal lawsuit on behalf of Native American tribes in Nebraska and South Dakota over the possible disruption of Indian artifacts.

The court is considering whether an obscure agency known as the Nebraska Public Service Commission must review the pipeline before it can cross the state, one of six on the pipeline's route. Gov. Dave Heineman gave the green light in 2013 without the involvement of the panel, which normally regulates telephones, taxis and grain bins.

The justices have given no indication when they will render a decision.

President Barack Obama has said he is waiting for the court's decision, and the White House on Tuesday threatened to veto the bill in what was expected to be the first of many confrontations with the new Congress over energy and environmental policy.