Police stand outside the Supreme Court in Washington, Thursday, June 23, 2016. (Evan Vucci/AP)

The Supreme Court on Thursday said that police must obtain a warrant before requiring a suspected drunk driver to submit to a blood alcohol test.

In a divided opinion, the court made a distinction between blood tests, which require the piercing of the skin, and breath tests, which it found are not particularly painful, intrusive or embarrassing.

The case arose after several states cracked down on drunk drivers by imposing criminal penalties, in addition to revoking licenses, for those who refuse to undergo testing when stopped by police. The question for the court was whether officers must obtain warrants to perform such tests.

In its opinion, the court tried to find a middle ground in balancing the government’s interest in promoting public safety on roads with individual privacy rights.

“The impact of breath tests on privacy is light, and the need for BAC [blood alcohol content] testing is great,” Justice Samuel A. Alito Jr. wrote for the court’s majority. He was joined by Chief Justice John G. Roberts Jr. and Justices Anthony M. Kennedy, Elena Kagan and Stephen G. Breyer.

In contrast, blood tests are “significantly more intrusive” and do not justify violating Fourth Amendment protections against unreasonable searches. The breath tests, Alito added, are “no more demanding than blowing up a party balloon.”

The court’s decision means that suspected drunk drivers can be arrested for refusing to submit to breath tests, but not for refusing a blood test.

The majority found that states are justified in trying to prevent drunken driving and pointed to statistics that show tougher laws corresponding with a decrease in alcohol-related fatalities from about 25,000 a year in the early 1980s to fewer than 10,000 in 2014. Alcohol consumption, Alito noted, is a leading cause of traffic fatalities and injuries.

During oral arguments in April, the attorney for three drivers from North Dakota and Minnesota said states cannot force people to give up their Fourth Amendment protection against warrantless searches.

Justice Sonia Sotomayor, joined by Justice Ruth Bader Ginsburg, agreed, finding that warrants should be required for both breath and blood testing.

Warrantless searches should be the exception, Sotomayor wrote.

“I fear that if the court continues down this road, the Fourth Amendment’s warrant requirement will become nothing more than a suggestion.”

Sotomayor said that the state’s interest in protecting the public from drunk drivers is accomplished by the arrest itself when the motorist is removed from the road.

But Alito responded that deterring people from getting behind the wheel in the first place with tough criminal penalties is just as important.

“License suspension alone is unlikely to persuade the most dangerous offenders . . . to agree to a test,” he wrote.

Government lawyers told the court during oral argument that judges are not always available to issue warrants and that some jurisdictions are more efficient than others. The majority concluded that the court system would be “swamped” if warrants were also required for breath tests and that local judges would have to be available at all hours of the day, seven days a week.

Sotomayor cast doubt on the amount of time it would take for officers to obtain warrants for breath tests and said such a requirement would only result in judges having to issue a few extra warrants per month.

The tests, she noted, are often conducted at police precincts rather than on the roadside — sometimes 40 minutes to two hours after arrest. That window, she said, could be used to obtain a warrant.

In a separate opinion, Justice Clarence Thomas called any distinction between the two types of tests an “arbitrary line in the sand.” Both tests are constitutional without a warrant, he wrote, in part because of the need for police to act quickly when collecting evidence that dissipates as the body metabolizes alcohol.

Advocates for stronger penalties said the court’s decision would make it easier for suspected drunk drivers to avoid punishment.

“Striking down criminal penalties for test refusal will result in more refusals, more plea bargains and tougher cases for prosecutors,” said Ralph Blackman, chief executive of the Foundation for Advancing Alcohol Responsibility.

For the drivers who challenged the state laws, the court’s ruling on Thursday has three distinct outcomes: The case of the North Dakota driver who refused a blood test is reversed; the case of the Minnesota driver who refused a breath test is affirmed; and the case of the North Dakota driver who consented to a blood test under false pretences is remanded to state court.

The cases are Birchfield v. North Dakota, Bernard v. Minnesota and Beylund v. Levi.