Activists have denounced a program that mandates the jailing of undocumented migrants as emblematic of the militarisation of the US-Mexico border.
Gathered outside Tucson's federal courthouse in Arizona on Friday, they said: "Operation Streamline has become a tangible symbol of the militarisation and the criminalisation of our communities."
Eduardo Garcia, of the human rights group SOA Watch, told EFE, these are "failures of due process for people who come to seek asylum in the US".
A "massive demonstration" against Trump's planned border wall was expected over the weekend.
Under Operation Streamline, launched in 2005, some undocumented migrants apprehended at the border have to serve jail time before being deported.
Before Streamline, unauthorised border-crossers were simply sent back to Mexico.
President Donald Trump's administration has announced that all undocumented migrants intercepted in the US Border Patrol's Tucson Sector would be processed under the Operation Streamline protocol.
This was regardless of whether they have criminal records or have been detained on previous attempts to enter the US.
A particularly controversial aspect of the Streamline program is the sentencing of dozens of migrants at a stroke in mass hearings at the Tucson federal courthouse.
Friday's demonstration was part of Border Encounter, an event organised by SOA Watch. Thousands of activists from the US, Mexico and Central America gathered in this Arizona city.
Participants protested outside the Eloy Detention Centre, the scene of more detainee deaths than any other migrant holding facility in the country.
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