(CNN) Two women speaking Spanish at a Montana gas station. A passenger on a Greyhound bus in Florida. A 10-year-old with cerebral palsy heading to a hospital in Texas.
Their brushes with Border Patrol occurred miles and months apart, but they have one thing in common: The authorities who detained them weren't working on the border.
The continental United States has two major land borders: a 1,933-mile stretch between the US and Mexico and a 3,987-mile stretch between the US and Canada.
But Border Patrol agents work in a far wider geographic area. According to federal regulations, the agency's expanded search authority to conduct immigration checks extends anywhere within a "reasonable distance" of 100 air miles from US land borders and coastlines.
"Without this authority, persons evading our immigration laws could effectively vanish after crossing," Daniel Hetlage, a spokesman for US Customs and Border Protection, said in a statement to CNN. "But with it, we have the ability to enforce our laws."
Two-thirds of the US lives inside this so-called 100-mile border zone, which includes several entire states, including Florida, Michigan, Maine and Hawaii, according to the American Civil Liberties Union.
Activists accuse the agency of racially profiling and violating constitutional rights as its enforcement efforts move inland.
"Although the 100-mile border zone is not literally 'Constitution free,' CBP frequently acts like it is," the ACLU says.
Conducting immigration checks in the 100-mile zone isn't a new practice, and this isn't a new debate. But it's been getting more attention lately as the Trump administration ratchets up its crackdown on illegal immigration.
Here's a look at several recent cases, and the issues they raise:
The case: Ana Suda says what started as a late-night trip to buy eggs and milk took a surprising turn last week in Havre, Montana, about 35 miles from the US-Canada border. Suda says a Border Patrol agent heard her speaking Spanish, then stopped her in the store and asked to see her ID. In a video Suda recorded of the incident, she asks why she and her friend were singled out and accuses the agent of profiling.
"It has nothing to do with that," the agent tells her. "It's the fact that it has to do with you guys speaking Spanish in the store in a state where it's predominately English-speaking."
Suda says she and her friend were both born in the United States and were allowed to leave the gas station after about 40 minutes.
The debate: Activists were quick to point out that there's nothing illegal about speaking Spanish in Montana or anywhere else in the United States.
In a statement, CBP said its agents "have broad law enforcement authorities," including the authority to question individuals, make arrests, and take and consider evidence.
Suda told CNN she's seeking help from the ACLU about the next steps she should take.
CBP says the incident is under review.
"Decisions to question individuals are based on a variety of factors for which Border Patrol agents are well-trained," an agency spokesperson said in a statement. "This incident is being reviewed to ensure that all appropriate policies were followed."
The case: Border Patrol agents boarded a Greyhound bus in Fort Lauderdale, Florida, in January, asking passengers to show identification. Video of the incident shows them questioning a woman, then taking her and her luggage off the bus.
A CBP spokesman told CNN affiliate WPLG that agents had identified a woman who'd overstayed her tourist visa. She was taken into custody and handed over to Immigration and Customs Enforcement.
"Border Patrol agents routinely conduct law enforcement activities at transportation hubs as part of a layered approach to preventing illegal aliens from traveling further into the United States," CBP said.
The debate: A fellow passenger's cell phone video of the arrest spread rapidly online. Experts were quick to point out that it's nothing new to see Border Patrol agents conducting immigration sweeps on buses or trains. But the video added fresh momentum to a push from advocates, who criticized the practice.
"Without an official judicial warrant, border patrol agents should not be permitted to board the private property of the Greyhound corporation to harass its customers and violate their civil liberties," the Florida Immigrant Coalition said in a statement at the time. "Floridians deserve to ride a bus in peace without having to carry a birth certificate or passport to go to Disney World, visit family, or commute for work."
Greyhound said its hands were tied.
"We are required to comply with all local, state and federal laws and to cooperate with the relevant enforcement agencies if they ask to board our buses or enter stations," the company said.
In a letter to Greyhound officials in March, the ACLU called for a policy change, listing the Florida incident along with similar cases in other states.
The ACLU argues that the bus company isn't legally required to let agents without warrants aboard, even in the 100-mile zone.
Greyhound, the letter said, "should not be in the business of subjecting its passengers to intimidating interrogations, suspicionless searches, warrantless arrests, and the threat of deportation."
The case: Advocates said 10-year-old Rosa Maria Hernandez, an undocumented immigrant, was on her way to emergency gallbladder surgery when Border Patrol agents pulled over the medical transport vehicle taking her through a checkpoint in Freer, Texas, about 60 miles from the border. Agents traveled with Rosa Maria to a hospital in Corpus Christi, Texas, and took her into custody after the surgery was completed.
Hernandez's family and their supporters characterized her detention as cruel and unnecessary. Immigration officials said the procedures were routine enforcement of the nation's immigration laws.
"Due to the juvenile's medical condition, Border Patrol agents escorted her and her cousin to a Corpus Christi hospital where she could receive appropriate medical care," CBP said in a statement after Rosa Maria was detained. "Per the immigration laws of the United States, once medically cleared she will be processed accordingly."
Rosa Maria was released from custody days after her apprehension.
The debate: CBP runs checkpoints like the one where Rosa Maria was detained along major thoroughfares and in other areas in the 100-mile zone throughout the Southwest.
Hetlage, the CBP spokesman, said checkpoints are vital for CBP's immigration enforcement efforts and "support the apprehension of criminal violators." The agency's authority to use them, he said, has been upheld by the Supreme Court.
To conduct a lawful search at checkpoints, agents must have probable cause developed from agent observations, records checks, canine sniffs and other methods, the agency says on its website.
Local activists routinely criticize checkpoints, alleging racial profiling and other civil rights violations. In Arizona, a group trying to monitor a checkpoint has been battling with the feds for years in court, trying to get access and data about what happens there.
Critics also claim checkpoints do little to help with immigration enforcement. They point to a recent General Accountability Office report which found only 2% of Border Patrol apprehensions occurred at checkpoints between fiscal year 2013 and 2016, and that 40% of drug seizures at checkpoints were 1 ounce or less of marijuana from US citizens.
"It really does affect border residents' lives day to day, if you live in this zone," says Chris Rickerd, policy counsel with the ACLU's national political advocacy department. But what happens at checkpoints, he says, should matter to all Americans -- no matter how close they live to the border.