In a dissent that cited W. E. B. Du Bois, James Baldwin and Ta-Nehisi Coates, Justice Sotomayor said the court had vastly expanded police power.

“The court today holds that the discovery of a warrant for an unpaid parking ticket will forgive a police officer’s violation of your Fourth Amendment rights,” she wrote. “Do not be soothed by the opinion’s technical language: This case allows the police to stop you on the street, demand your identification and check it for outstanding traffic warrants — even if you are doing nothing wrong.

“If the officer discovers a warrant for a fine you forgot to pay,” she continued, “courts will now excuse his illegal stop and will admit into evidence anything he happens to find by searching you after arresting you on the warrant.”

Justice Sotomayor added that many people were at risk. Federal and state databases show more than 7.8 million outstanding warrants, she wrote, “the vast majority of which appear to be for minor offenses.” There are, she added, 180,000 misdemeanor warrants in Utah. And according to the Justice Department, about 16,000 of the 21,000 residents of Ferguson, Mo., are subject to arrest warrants.

Justice Ruth Bader Ginsburg joined most of Justice Sotomayor’s dissent, along with all of a separate dissent from Justice Elena Kagan. But Justice Sotomayor reserved her most personal reflection for a part of her dissent in which she wrote only for herself, setting out in detail the dangers and indignities that often accompany police stops.

“For generations,” she wrote, “black and brown parents have given their children ‘the talk’ — instructing them never to run down the street; always keep your hands where they can be seen; do not even think of talking back to a stranger — all out of fear of how an officer with a gun will react to them.”

“We must not pretend that the countless people who are routinely targeted by police are ‘isolated,’” she wrote. “They are the canaries in the coal mine whose deaths, civil and literal, warn us that no one can breathe in this atmosphere. They are the ones who recognize that unlawful police stops corrode all our civil liberties and threaten all our lives. Until their voices matter, too, our justice system will continue to be anything but.”

Justin Driver, a law professor at the University of Chicago, said Justice Sotomayor’s dissent was remarkable. It is, he said, “the strongest indication we have yet that the Black Lives Matter movement has made a difference at the Supreme Court — at least with one justice.”