Washington (CNN) Attorney General Jeff Sessions continued his efforts to tighten control of the immigration courts with two quiet moves Tuesday night, even as President Donald Trump said he was "not happy" with Sessions on immigration.

In one decision, Sessions further constrained the discretion of immigration judges to show leniency to undocumented immigrants. In the other, he signaled he may restrict the ability of immigrants awaiting asylum hearings to be let out of detention.

The moves are the latest in a series of steps Sessions has taken to assert his authority over the immigration courts and thus the way immigration law is enforced in the US. The immigration judges' union and the national association for immigration lawyers have decried the moves as threatening the due process rights of immigrants and the independence of judges, while immigration hardliners have hailed Sessions as restoring immigration laws to their original intent.

The moves also come as Trump, who campaigned largely on his aggressive immigration views, has repeatedly attacked his attorney general publicly, including in an interview with Hill.TV on Tuesday. In the interview, Trump lamented Sessions' recusal from the Russia investigation and said he was dissatisfied on immigration.

"I don't have an attorney general. It's very sad," Trump said, according to Hill.TV. "I'm not happy at the border. I'm not happy with numerous things."

Sessions, however, has been at the forefront of the administration's aggressive immigration agenda, especially in using his unique authority to single-handedly overrule the immigration courts' appellate body and issue interpretations of immigration law. Those binding rulings must be followed by the nation's nearly 400 immigration judges, who are technically employees of Sessions and the Justice Department under US law.

On Tuesday, Sessions used that authority to refer himself more cases so he could rule on them.

In a pair of linked cases, Sessions ruled that immigration judges are not allowed to use their discretion to terminate or dismiss cases. Under the ruling, only if the Department of Homeland Security decides it no longer wants to pursue the case or the immigrant achieves or proves a legal right to stay in the US can a judge dismiss their deportation case. Judges may not simply decide the case is not worth pursuing further.

The move follows a similar ruling Sessions made earlier this year that judges are not allowed to use their discretion to close cases either. Closure effectively ends proceedings but doesn't dismiss the case altogether.

"The authority to dismiss or terminate proceedings is not a free-floating power an immigration judge may invoke whenever he or she believes that a case no longer merits space on the docket," Sessions wrote.

The executive director of the American Immigration Lawyers Association, Benjamin Johnson, called the decision "part of a systematic effort to marginalize the role of immigration judges in their own courtrooms" in a statement.

"Time and time again the Attorney General's actions have shown us that an immigration court system housed under the Department of Justice cannot be one that guarantees due process," Johnson's statement said, and he called for the immigration courts to be established as an independent institution outside of the Justice Department.

National Association of Immigration Judges President Ashley Tabaddor told CNN the use of Sessions' authorities to curtail judges' discretion was "concerning" as part of a broader use of the immigration courts to align with the administration's policy priorities.

"It's just another way of putting more pressure and increasing the backlog and the pressure on judges to just to do more cases and faster with limited resources and limited tools," Tabaddor said. "It's another representation of the improper use of the court as an extension of the law enforcement policies of the executive branch."

Also on Tuesday, Sessions signaled he may be inclined to keep asylum seekers in detention while they await their hearings.

The attorney general has not made a decision yet, but he referred himself a case that would consider whether asylum seekers are entitled to bond hearings. He invited interested members of the public to submit arguments to him about it by Oct. 16.

The question Sessions poses is whether an immigration appeals court ruling from 2005 should be overturned, a decision that found that immigrants who pass the first interview threshold to pursue the right to stay in the US under asylum law are entitled to bond hearings and potential release from custody.

If Sessions were to decide that immigrants are not eligible for such hearings, tens of thousands of them could be kept in detention while their cases are being heard.

The administration and its supporters argue that keeping more immigrants in detention will prevent them from absconding into the US and disappearing from authorities, thus deterring more immigrants from coming to the US illegally.

But immigration advocates argue that such moves are designed to undercut the ability of immigrants to seek lawful protections in the US. It is much harder to obtain legal representation in detention, attorneys argue, and immigrants are not guaranteed legal representation in court. Additionally, with asylum law's complexities, advocates warn that the rapid pace of cases in detention courts make it more difficult for the immigrants to build their cases.