Washington (CNN) The Trump administration quietly made it more difficult for immigrants to seek asylum in the US last month, the latest in a series of steps designed to deliver on the President's campaign promise to harshly enforce immigration laws.

Supporters of President Donald Trump's policies say the move cuts off an incentive for migrants to make their way to the US, where they are granted the chance to pursue asylum claims and sometimes build underground lives illegally.

But advocates for immigrants say the changes could block people fleeing genuinely violent situations -- especially vulnerable women and children -- from getting protections or even adequately having their cases heard.

The move came without the fanfare of Trump's executive orders and implementation guidance, tucked away in arcane guidance for asylum officers distributed by US Citizenship and Immigration Services to officers and immigration lawyers.

But despite the changes being widely unnoticed, experts say they have major implications for how would-be asylum seekers' cases are handled. Taken with the rest of Trump's actions to crack down on illegal immigration and tighten border security, the changes could further restrict the flow of immigrants into the US without needing to change any laws.

"Clearly a signal is being given to the field here: We want to be stricter," said former USCIS Director Leon Rodriguez, who served in the role for the last two-and-a-half years of the Obama administration and is now an attorney. "I think the intent of it will absolutely be understood by the officers."

The changes came in an updated lesson plan for asylum officers distributed by USCIS Asylum Division Chief John Lafferty on February 13. They went into effect February 27.

USCIS declined to comment on the guidance, referring to previously published memos from DHS explaining Trump's orders writ large.

The document was provided to CNN by Tahirih Justice Center, an organization that defends immigrant women and children fleeing violence, who received it as members of the American Immigration Lawyers Association's national asylum committee.

"The lesson plan is a disappointing shift for the Asylum Division, the part of our government tasked with implementing asylum law and protecting refugees, the most vulnerable people in the world," said Archi Pyati, chief of policy and programs at Tahirih. "Victims of violence who meet the definition of a refugee will be unfairly turned away before they've even talked to a lawyer, counselor, or judge. That is not due process. That is not protection. That is not American."

'Credible fear'

The issue at stake is what's known as "credible fear." When an immigrant arrives at the US without authorization to enter, he or she can make a claim that he or she is fleeing persecution or torture, and thus is entitled to asylum in the US under the law.

Eventually, an immigration judge decides whether or not a person is entitled to asylum. But the first step is an interview with an asylum officer, who determines whether the person has a credible fear of persecution or torture and thus can continue in the immigration courts.

In fiscal year 2016, nearly 80% of credible fear cases nationwide were granted, letting more than 73,000 asylum seekers pursue their cases in the US.

But the actual asylum hearing can sometimes be years in the future, and often the immigrants are paroled into the US and build lives as they await their hearing. Some do not arrive for their proceedings, and a substantially lower percentage of cases are eventually granted asylum than those that are granted credible fear.

Immigration conservatives have long targeted this process for letting in undocumented immigrants, decrying what they call "catch and release" -- a policy Trump has vowed to end by increasing detentions and deportations of immigrants.

Changes to the lesson plans for credible and reasonable fear may seem minor to most Americans. For example, the new guidance removes a passage from the previous version that said if an asylum officer has reasonable doubt about a person's credibility, they should likely find credible fear and allow an immigration judge to hear the question at a full hearing.

How to assess credibility

In another change, a passage has been altered on individuals' "demeanor, candor, and responsiveness" as a factor in their credibility. Both the 2017 and 2014 versions note that migrants' demeanor is often affected by cultural factors, including being detained in a foreign land and perhaps not speaking the language, as well as by trauma sustained at home or on the journey to the US.

But the new version removes guidance that said these factors shouldn't be "significant factors" in determining someone's credibility -- essentially allowing asylum officers to consider signs of stress as a reason to doubt someone's credibility.

That provision especially worries supporters of a less restrictive credible fear threshold, who argue that the US should risk letting in more migrants than possibly rejecting applicants who genuinely risk death and violence when they're turned away. At minimum, they say, the determination should be done by an immigration judge with access to legal counsel for the immigrant making his or her case.

"These are very quick determinations made without any counsel by people who have just arrived and are exhausted, still traumatized and often not fluent in the language," said Washington University law professor Stephen Legomsky, who served as chief counsel to USCIS under President Barack Obama.

A former DHS official who requested anonymity to speak freely said that changes to tighten the credible fear threshold were considered in the last administration, but not pursued.

Legomsky acknowledged that with 80% of cases resulting in credible fear findings, it is possible that changes are needed, but he argued that a better solution would be to increase the capacity of the immigration courts to hear cases more quickly.

Trump's executive orders do call for more immigration judges, though numbers are not specified and the provision is not emphasized.

In a Q&A explaining Trump administration changes, DHS said its goal was "to ensure the asylum process is not abused."

Jessica Vaughan, policy director of the conservative immigration policy Center for Immigration Studies, which advocates for lower immigration, hailed the move, saying the move will help "restore integrity" to the system for legitimate asylum seekers.

"I think these are important steps because in recent years the system has been set up to favor the applicant and to put the thumb on the scale in favor of the applicant and to make it harder for an asylum officer to reject the claim, even in cases of reasonable doubt or credibility," Vaughan said. "There's been a very remarkable increase in the number of people asking for asylum in the last five or six years or so, and ... it looks very much like people were trying to take advantage of a very lenient system and one they would not be penalized for using and that motivates illegal immigration and harms the integrity of our legal immigration system."

Rodriguez says the way asylum officers are actually trained on the new lessons will be key. While the message being sent seems to be that officers should let in fewer asylum seekers, it depends on the implementation.

"A lot of this really depends on how this actually translates in the field," Rodriguez said. "I think this could be seen as some mild tightening to sort of incrementally tighten the process, but depending on how this is taken in the field, it could amount to a drastic tightening."

CORRECTION: This story has been updated to correct the spelling of Jessica Vaughan's name.