WASHINGTON — Border Patrol officers are working without permission on private property and setting up checkpoints up to 100 miles away from the border under a little-known federal law that is being used more widely in the Trump administration’s crackdown on illegal immigration.

In Texas, a rancher has accused the Border Patrol of trespassing after he said he found a surveillance camera the agency placed on his property.

In New Hampshire, border officers working with state officials conducted what the American Civil Liberties Union described as illegal drug searches after residents were arrested at immigration checkpoints set up on Interstate 93. One of the checkpoints was set up just before a local marijuana festival.

And recently in Florida, New York, and Washington state, Border Patrol officers have been criticized for boarding buses and trains to question riders — mostly American citizens — about their immigration status.

Trump administration officials defend the government’s decades-old authority to search people and property, even without a warrant, far from the border. They call it a vital part of preventing weapons, terrorists, and other people from illegally entering the United States.

Officials conceded that some of the searches — particularly those aboard Greyhound buses or Amtrak trains on domestic routes — had increased since the Obama administration. Under President Trump, field supervisors have regained the authority to order the searches, instead of officials at Border Patrol headquarters in Washington.

“The US Border Patrol conducts transportation checks in accordance with the law,’’ said Stephanie Malin, a spokeswoman for Customs and Border Protection, which oversees the Border Patrol.

The agency is an arm of the Department of Homeland Security, which would not provide statistics on how often, or where, it checks domestic travel passengers or patrols on private property.

Many of the searches turned up marijuana and other drugs, according to agency ­data. But most of the drugs were seized in small quantities — about an ounce or less — and they were taken from American citizens in 40 percent of the cases.

The department said in a statement that the checkpoints were “strategically placed where illegal cross-border smuggling is most likely to converge.’’

Stephen I. Vladeck, a professor at the University of Texas School of Law, said the department had occasionally pushed the limits of its authority to conduct searches without a warrant far from the border.

“Inevitably, one of these cases is going to get to the Supreme Court, which will have to revisit the seemingly limitless government authority the department claims it has,’’ ­Vladeck said. “It cannot be that anyone who lives or travels within 100 miles of the border has no Fourth Amendment rights.’’

The Fourth Amendment protects against unreasonable searches and seizures.

Current federal immigration law does not require the government to obtain a warrant before searching people and their property at ports of entry. Once away from a land or maritime border, but still within what the Justice Department has defined as a “reasonable distance’’ of 100 miles, officers can search people who are suspected of immigration violations and smuggling drugs.

But many border residents and travelers say that authority amounts to an invasion of privacy.

An estimated 200 million Americans live within 100 miles of the border, according to the American Civil Liberties Union. At least 11 states — mostly in the Northeast — are either entirely or almost entirely in the 100-mile radius.

A measure to limit that distance to 25 miles passed the Senate in 2013 but was rejected by the House; it was proposed after Senator Patrick Leahy, a Vermont Democrat, was stopped by the Border Patrol at an immigration checkpoint.

The legal dispute in Texas challenges the Border Patrol’s authority to search private property without permission. By law, officers can go onto private property within 25 miles of the border without permission from the owner. The lawyer for Ricardo D. Palacios said his property, Juan Salinas Ranch, is more than 30 miles from the border.

Gilles Bissonnette, legal director for New Hampshire’s ­ACLU chapter, said the Border Patrol violated state law by conducting drug searches. He said that New Hampshire courts have held that without a warrant, authorities cannot deploy drug-sniffing dogs in searches — as they were at the checkpoints — without a reasonable suspicion of a crime.

“They were supposed to be conducting immigration checks,’’ Bissonnette said.