The Biden administration has ordered U.S. immigration enforcement agencies to stop using terms such as “alien,” “illegal alien” and “assimilation” when referring to immigrants in the United States, a rebuke of terms widely used under the Trump administration.

The change was detailed in memos sent Monday to department heads at Immigration and Customs Enforcement and Customs and Border Protection, the nation’s chief enforcers of federal immigration laws, according to copies obtained by The Washington Post. It is part of an ongoing effort to reverse President Donald Trump’s hard-line policies and advance President Biden’s efforts to build a more “humane” immigration system.

Among the changes: “Alien” will become “noncitizen or migrant,” “illegal” will become “undocumented,” and “assimilation” will change to “integration.”

The memos also send a clear signal to a pair of law enforcement agencies — and their associated labor unions, which endorsed Trump’s presidential candidacy — that under the Biden administration, their approach must change.

“As the nation’s premier law enforcement agency, we set a tone and example for our country and partners across the world,” Troy Miller, CBP’s top official, said in his memo. “We enforce our nation’s laws while also maintaining the dignity of every individual with whom we interact. The words we use matter and will serve to further confer that dignity to those in our custody.”

Acting ICE director Tae Johnson echoed those words in a separate memo, saying, “In response to the vision set by the Administration, ICE will ensure agency communications use the preferred terminology and inclusive language.”

The new guidance mirrors an earlier directive from U.S. Citizenship and Immigration Services (USCIS), which processes green cards and citizenship applications, and applies broadly to agency communications, including internal correspondence and public information. Officials said the changes take effect immediately.

Border Patrol agents and ICE routinely use “alien” and “illegal” on social media, in news releases and in memos to refer to people they take into custody for allegedly violating civil immigration laws or crossing the border illegally. In the past, officials and some federal judges have defended using “alien” because it is the official definition of noncitizen in federal laws. Officials acknowledge that officials may need to use the terms in “legal or operational documents,” such as when filling out required forms.

Noncitizens include immigrants who are in the United States illegally, as well as millions of legal permanent residents, also known as green-card holders, and visitors arriving on visas for work or tourism.

Advocates for immigrants, who have increasing influence on the White House, say the terms are archaic and dehumanizing — “alien,” for instance, is more likely to conjure visions of space creatures than people, they say — and should be scrapped in favor of a more civil tone.

Republicans slammed the agencies’ new lexicon as imprecise and a sign that the Biden administration is pulling back on immigration enforcement as a large influx of migrants arrive at the southwest border.

“We use the term ‘illegal alien’ because they’re here illegally,” Sen. Tom Cotton (R-Ark.) said on Twitter. “This kind of weakness and obsession with political correctness is why we’re having a crisis on the border in the first place.”

House Minority Leader Kevin McCarthy (R-Calif.) tweeted: “President Biden is more concerned about Border Patrol’s vocabulary than he is about solving the border crisis. These backwards priorities are only making the situation worse.”

Democrats and advocates for immigrants praised the new policy. “Words matter,” tweeted Rep. Jesús “Chuy” García (D-Ill.), calling the new terms “a small but important step.”

Jose Antonio Vargas, founder of Define American, a nonpartisan organization that has pushed for such changes, said in an interview that Democrats must turn words into actions and pass a bill to give legal status to millions of undocumented immigrants.

“The Trump administration used language as a weapon,” said Vargas, an undocumented immigrant from the Philippines and a former Post reporter. “This administration is using language as a bridge — a bridge to what exactly? If you’re going to use humanizing language, then how does that lead to policies — specific, tangible, policy changes — that treat immigrants as people?”

Biden proposed eliminating the term “alien” from federal immigration laws in the citizenship bill he sent to Congress on his first day in office. The White House has said that replacing “alien” with “noncitizen” recognizes the United States as “a nation of immigrants” — a phrase the Trump administration had struck from the USCIS mission statement.

Federal officials say the shifting language is not merely symbolic but part of a broader effort to reorient agencies that became highly politicized under Trump. His orientation of the agencies was widely lauded by Republicans but reviled by many liberal Democrats.

Trump lavished praise on immigration and border agencies during his presidency and urged Congress to significantly expand their ranks. He allowed ICE to arrest anyone who was in the United States illegally, reversing Obama-era restrictions that sought to spare undocumented immigrants who had no criminal records from being deported. And he expanded the barrier on the southwest border with the aim of aiding Border Patrol agents.

Biden has rolled back many of Trump’s hard-line policies, such as limiting the immigrants ICE is allowed to detain to those deemed national security threats, recent border crossers and people with an aggravated felony conviction.

But he has resisted calls from liberal Democrats to abolish ICE, and Homeland Security Secretary Alejandro Mayorkas has praised CBP’s efforts to contend with the surge of migrants at the southwest border.

Scrapping the term “alien” has been debated in state and local governments as well as the courts, where some judges have used it in rulings and others have not.

California — where 27 percent of the population are immigrants, including naturalized citizens — passed a state law in 2015 banning the use of the term “alien” in the labor code. A Democratic legislator filed a bill in February that would forbid the term in all manner of state laws in areas such as housing, education, natural resources and driver’s licenses.

The bill says laws should refer to noncitizens in other ways, such as “a person who is not a citizen or national of the United States.”