Documents obtained by the American Civil Liberties Union (ACLU) show that the U.S. Immigration and Customs Enforcement is considering proposals to expand its immigration detention capacity in at least eight states.

Why it matters: The proposals going back to September show that the Biden administration was preparing for its own expanded detention of immigrants while Democrats attacked President-elect Trump for his mass deportation plan.

The big picture: The plans could give Trump a head start to launch the largest mass deportation effort in U.S. history once he takes office since detention is the most costly and labor-intensive piece of deportation.

Zoom in: The ACLU said Wednesday that documents obtained through an open records request show proposals sought expansion of detention capacity in Michigan, California, Kansas, Nevada, New Jersey, New Mexico, Texas, and Washington state.

• They reveal that private prison corporations — and other companies that provide services to build temporary facilities, monitor compliance and staff facilities — submitted proposals for expanded immigration detention in response to ICE's contract requests.

• Documents show GEO Group, Inc., CoreCivic, Management and Training Corporation (MTC) and Target Hospitality, which provides temporary tent facilities, submitted proposals.

Zoom out: The proposals mentioned the North Lake Correctional Facility in Baldwin, Michigan, which is owned and operated by the GEO Group, Inc.

• Also cited was the Rio Grande Processing Center in Laredo, Texas, owned and operated by the GEO Group, Inc.

• Carrizo Springs, a tent facility previously used to detain immigrant minors in Carrizo Springs, Texas, owned by Target Hospitality, was also mentioned.

An ICE spokesperson did not immediately respond to an email from Soixa.

What they're saying: "These records only further confirm ICE's work to expand immigration detention across the country," Eunice Cho, senior staff attorney at the ACLU's National Prison Project, said in a statement.

• Cho said this includes in facilities "with clear records of abuse" and in areas where immigration detention has not previously existed.

• "Expansion of detention will only enable ICE to enact President-elect Donald Trump's plans for mass deportation."

Between the lines: The documents show that the Biden administration, just like the Obama administration, was involved in outlining its own stepped-up deportation plan while attacking Republicans for suggesting the same.

• Immigrant rights groups have criticized Trump's mass deportation plan and said it would strike fear in communities across the country.

• But many of the same groups have been reluctant to attack President Biden or Vice President Harris.

• Harris said she supported a bipartisan crackdown on immigration and border security, drawing criticism from smaller grassroots immigrant advocacy groups.

State of play: U.S. immigration courts are on pace to decide record numbers of deportation cases — and order the most removals in five years — under Biden's push to fast-track asylum decisions.

• U.S. Immigration and Customs Enforcement deported more than 271,000 people last fiscal year — the most in nearly a decade, according to an annual report released last month.

The intrigue: The discovery comes just weeks after the ACLU received its first and second tranche of FOIA documents revealing that ICE is considering expanding detention facilities in several states.

By the numbers: ICE currently only has around 38,000 people in detention — prioritizing noncitizens the border patrol arrested at the Southwest Border and noncitizens with criminal histories, according to ICE's annual report.

• To hold more people from a raid surge would require a mass building project of "soft detention" centers, or temporary ad hoc facilities, to house people.

What we're watching: The Trump administration can act on the proposals from the Biden administration and seek more.