WASHINGTON -- In 2010, when the Supreme Court ruled that criminal defense lawyers must warn their clients if deportation could be a consequence of a guilty plea, Justice Samuel A. Alito Jr. made a prediction.
The ruling, he wrote in a concurrence, "will lead to much confusion and needless litigation."
On Thursday, the prediction was at least partly vindicated in a complex argument over whether the ruling should apply retroactively to thousands of people whose convictions became final before it was issued.
The new case involved Roselva Chaidez, a Chicago woman from Mexico who has been a legal permanent resident of the United States since 1977. In 2003, she was accused of participating in an insurance fraud by falsely claiming to have been a passenger in a car involved in an accident.
She pleaded guilty and was sentenced to four years of probation. Her lawyer failed to tell her that the plea made her eligible for deportation.
The question for the justices was whether Ms. Chaidez could take advantage of the 2010 ruling, Padilla v. Kentucky. The answer largely turned on whether Padilla announced a new legal principle or merely applied an old one, a distinction made in a 1989 decision, Teague v. Lane. If a decision merely applies existing precedent, it is retroactive. New rules only count from when they are announced.
Ms. Chaidez's burden of persuading the justices to apply Padilla retroactively was not made easier by the array of opinions in it. Five justices said lawyers had an affirmative obligation to tell clients about the possibility of deportation. Justice Alito, in his concurrence, which was joined by Chief Justice John G. Roberts Jr., said only that lawyers should not say anything false. Justice Alito called the majority's approach a "dramatic departure from precedent," a problematic statement for Ms. Chaidez.
Justice Antonin Scalia, in a dissent joined by Justice Clarence Thomas, said there was no constitutional right to accurate legal advice about the collateral consequences of a criminal conviction.
At Thursday's argument, Justice Scalia conceded that a fractured decision did not necessarily mean that it announced a new principle.
"I'm sure you're right," he told Jeffrey L. Fisher, a lawyer for Ms. Chaidez, "that the mere fact that there was a dissent in the case that adopted the rule does not necessarily make it a new rule. But you, on the other hand, would agree, would you not, that those who dissented from that case would regard it as a new rule?"
Calling it "a tricky question," Mr. Fisher said Justice Scalia might reconsider his earlier position.
Michael R. Dreeben, a lawyer for the federal government, started his argument with an apparent concession. Had the court adopted Justice Alito's position and limited the sweep of Padilla to bad advice as opposed to no advice, Mr. Dreeben said, the court would probably not have announced a new principle.
What the court actually decided, however, he said, was "a dramatic expansion and upheaval in Sixth Amendment law," which governs the right to counsel in criminal prosecutions.
Justice Stephen G. Breyer suggested that the court might have made things needlessly complicated. "I would have thought it was common sense that a lawyer should tell the client the terrible things that are going to happen to him if he pleads guilty," he said.
The Supreme Court does not usually sit on Thursdays. The argument in the case, Chaidez v. United States, No. 11-820, was originally set to be heard Tuesday but was rescheduled in light of Hurricane Sandy.
This article originally appeared in The New York Times.