Attorney General William Barr issued two decisions limiting immigrants' options to fight deportation late Friday, furthering the Trump administration's immigration crackdown.

The little-noticed decisions, made through the attorney general's unique "certification" power, remove a long-standing path to stop deportation for people with old criminal convictions and disqualify people with multiple drinking and driving convictions from many paths to legal immigration status.

Advocates worry these decisions could push more immigrants into the deportation system while giving them fewer avenues to fight to stay.

"Hundreds of thousands of immigrants throughout the United States are going to be impacted by these decisions," said Rose Cahn, a senior attorney with the Immigrant Legal Resource Center, who works with immigration advocates around the country. "This is one tactic out of many that we are seeing the federal government use to make life for immigrants as unpleasant as possible."

Barr can make such sweeping decisions over immigration law because unlike most of the federal court system, immigration court is part of the executive branch, not the judiciary, and is housed within the Department of Justice. That makes the attorney general both the nation's top prosecutor and, in the case of immigration courts, its top judge.

As top judge, Barr 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 on how immigration courts should interpret the law.

While past administrations have used the power, often to narrowly clarify immigration law, the Trump administration has been using it to alter large parts of the immigration system without writing new laws or regulations. Since coming into office, Trump's attorneys general have used the certification process on a range of immigration issues, including limiting the discretion of immigration judges and narrowing asylum law by restricting the number of migrants who can stay in the U.S.

Barr's new decisions establish that he is following in the footsteps of his predecessor, Jeff Sessions, by using certification to overturn sometimes decades-old precedent and limit paths to legal residency. Sessions issued decisions on five cases during his tenure. Barr has now issued four. The Trump administration, not yet three years old, is on track to issue more of these decisions than any administration in recent history. In its eight-year span, the Bush administration issued 16 decisions. The Obama and Clinton administrations issued four and three respectively.

The Justice Department declined to comment.

The two new decisions focus on immigrants with criminal convictions. In the first, Matter of Castillo-Perez, Barr ruled that two or more Driving Under the Influence convictions disqualify an immigrant from having "good moral character."

DUIs are the most common criminal conviction for people arrested by Immigration and Customs Enforcement, according to federal data obtained by Syracuse University's Transactional Records Access Clearinghouse. They are among the most common crimes in many states, and are not deportable offenses on their own.

The "good moral character" standard is used throughout the immigration system. Immigrants must prove they have had good moral character for a set period of years when requesting cancellation of a deportation order and in applying for citizenship, among other immigration processes.

Immigration attorneys expressed outrage at how many people would be barred from using those processes under the new decision.

"The attorney general makes no clear distinction between a misdemeanor or felony DUI, or between a recent DUI or one that took place several years ago," said Raha Jorjani, director of the immigration representation unit of the Alameda County public defender's office. "This decision will separate more families."

Rehabilitation efforts after DUI convictions, such as going sober, completing alcohol-safety programs and attending Alcoholics Anonymous meetings, "are commendable, but they do not themselves demonstrate good moral character," Barr wrote in his decision, and do not counteract the disqualifying DUI convictions.

Dan Cadman, a former immigration official and current fellow at the Center for Immigration Studies, which advocates for limiting immigration, applauded the decision.

"This sounds more like an application of common sense than a dastardly attempt to do an end-run on aliens' due process rights," Cadman said. "The public needs to keep firmly in mind that these two certifications involve aliens convicted of serious crimes who were seeking to evade removal from the United States."

The second decision, in Matter of Thomas and in Matter of Thompson, decreases the ability of state courts to influence the federal deportation process through adjusting old low-level criminal sentences.

In recent years, some states, including New York and California, passed laws to ensure low-level crimes do not unintentionally trigger a deportation order for immigrants. A few also have processes to retroactively shorten old low-level criminal sentences to below the immigration system's criteria for deportation (typically a one year sentence or longer).

Progressive prosecutors around the country, many of them recently elected, have been pushing for potential immigration consequences, like deportation, to be taken into account at the beginning of a local criminal case. Some have even added immigration attorneys to their staff to help with those efforts.

Brooklyn District Attorney Erik Gonzalez was one of the first to do so. He and 42 other state and local elected prosecutors filed an amicus brief in the Thomas and Thompson case, arguing that the federal government should recognize the decisions they make when retroactively changing a sentence.

A refusal to do so "would undermine the role of prosecutors in the criminal justice system and the sovereignty of states to enforce their criminal laws and exercise prosecutorial discretion," they wrote.

For years, those sentence modifications were accepted by immigration judges. Barr's decision changes that, limiting which modifications can count in immigration court. To count, a modification must be specifically because of an error in the procedure of the case, not to avoid deportation.

"What this is is a real shot fired against states who are leading the effort to bring the federal immigration consequences in line with the intended consequences of state offenses," Cahn said.

The Obama administration did not prioritize lower-level old deportable offenses, but the Trump administration has made no such distinction. In the past three years, residents of many decades whose offenses date from the 1990s have found themselves in immigration court. Some, like many Southeast Asians who came to the U.S. as refugee children after the Vietnam War, are fighting to stay in the country that is the only home they've ever known.

Though the paths to fight deportation are narrowing, there are still other options. Outside of the courts, immigrants can request a governor's pardon for old crimes, but those are rare and can take months — time immigrants may not have before deportation.

Immigration lawyers have appealed many of the Trump administration's previous certification decisions to federal appeals courts. Cahn said the administration can expect a fight on these new decisions as well.