A Monday ruling by Attorney General William Barr that limited the ability of migrants to seek asylum in the United States is the latest example of the Trump administration's use of a unique power of the attorney general's office to reshape immigration law.

Barr used a process called "certification" to issue a decision Monday that closes the door on most asylum-seekers who fear persecution due to family ties, overturning years of precedent.

The case involves a Mexican man who said he was threatened by gangs when his father refused to let them use his store. U.S. law requires asylum-seekers to prove they fear persecution based on race, religion, nationality, political opinion or membership in a "particular social group." The Board of Immigration Appeals determined that the man's family constituted a social group.

Barr reversed that finding, writing that a family does not qualify as such a group just because it is being persecuted. His ruling will now lower the number of migrants who are eligible for asylum.

Since coming into office, Trump's attorneys general have used the certification process to both limit the discretion of immigration judges and narrow asylum law, restricting the number of migrants who can stay in the U.S.

"All of these things fit into the same master plan of trying to force judges into becoming this kind of assembly line for issuing deportation orders," Jeffrey Chase, a former immigration court judge, said.

Barr was able to reshape the law because the immigration courts, where migrants must make their case for asylum, have a unique structure.

Most federal courts are part of the judicial branch, but immigration courts are part of the executive branch, and are thus controlled by the Justice Department. The attorney general, who runs the department, is both the nation's top prosecutor and, in the case of immigration courts, its top judge.

Because Barr is the top judge, he can essentially pluck cases from the Board of Immigration Appeals, which is effectively the appellate arm of the immigration courts, for "certification." After reviewing those cases, he can issue binding rulings.

Past attorneys general have used this power. During President George W. Bush's eight years in office, 16 such decisions were issued, the most of any administration since the late 1950s. Under President Barack Obama, there were four such rulings, and under President Bill Clinton there were three.

But the Trump Justice Department is on pace to outstrip any prior administration in rendering these rulings. Its three attorneys general have issued decisions in seven cases in the last two and a half years. Three are pending.

Curbing asylum

Certification can be an important tool in resolving legal questions and clarifying complex matters of law, said Dan Cadman, a former immigration official and current fellow at the Center for Immigration Studies, which advocates for limiting immigration.

He added that while decisions are officially written by the attorney general alone, "[he] relies extensively on the expertise of various attorneys within his own staff."

But critics believe the system puts too much power in the hands of the nation's top prosecutor.

"It's a very dangerous practice," Stephen Legomsky, a law professor at Washington University in St. Louis and the former chief counsel for U.S. Citizenship and Immigration Services under Obama. "It should be judges and not politicians, and certainly not prosecutors, who should be deciding individual cases."

Early in his tenure, former Attorney General Jeff Sessions issued a decision in a case called Matter of A.B. that claimed most immigrants fleeing domestic and gang violence did not qualify for asylum. The application of that decision is now being challenged in a federal lawsuit.

The decisions have also affected the daily workings of the court. Sessions eliminated the ability of judges to administratively close cases, a tool they had often used to move dockets along more quickly.

"He took away a docket management tool that has been recognized for over 40 years and essentially just reversed it at the drop of a hat," Judge Ashley Tabaddor, president of the National Association of Immigration Judges, said.

That single decision could lead to 350,000 closed cases returning to a court system that already has a backlog of more than 900,000 cases.

Barr, who took over from acting Attorney General Matthew Whitaker in February, made the first of his rulings in June, limiting the ability of detainees to bond out of detention. That ruling is also being challenged in court.

The most recent case of the Mexican man seeking asylum is also likely to be fought out in court. There is a long history of the courts recognizing families as a particular social group, so Barr's latest decision could be overturned in the district courts, according to Jeremy McKinney, second vice president of the American Immigration Lawyers Association.

But for now, the case could mean hundreds or thousands of those arriving at the border with claims of being targeted due to family ties do not qualify for protection.

"I think that the impact of today's decision will be very large in the short term," McKinney said.

The Justice Department and the Executive Office of Immigration Review, a subdivision of the department that runs the Board of Immigration Appeals, declined to comment.