Scott Warren faces up to 20 years in prison if convicted of harbouring two undocumented migrants in Arizona.

An Arizona activist charged with harbouring two undocumented migrants faces trial on Wednesday in a case likely to set a precedent over what aid US citizens can give to undocumented migrants.

United States Border Patrol agents arrested Scott Warren in a January 2018 raid near Ajo, Arizona after they found two migrants hiding in the shower of a ramshackle building used by humanitarian groups.

The 36-year old faces two felony counts of harbouring the undocumented migrants and one felony count of conspiracy to transport the two men. The university geography instructor could face up to 20 years in prison if convicted of all charges.

Warren was indicted after former US Attorney General Jeff Sessions instructed prosecutors to prioritise cases involving the harbouring of migrants. The crackdown was part of President Donald Trump‘s “zero-tolerance” policies at the border.

Warren is a volunteer for No More Deaths, a faith-based group providing water, food and medical aid to migrants in the harsh deserts of southern Arizona.

Thousands died crossing the border

More than 3,000 undocumented migrants have died since 2001 trying to cross the area where temperatures can exceed 115 Fahrenheit (46 Celsius), according to Pima County Office of the Medical Examiner data.

Warren was arrested the same day No More Deaths published a video showing US Border Patrol agents destroying water supplies the group left for migrants.

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Warren’s lawyers argue the arrest was in retaliation for the video. They say he was lawfully exercising his religious beliefs and rights to help the migrants after they spent two days crossing the desert.

His parents have collected over 128,000 signatures calling on the US Attorney’s Office in Tucson to drop all charges.

“This is an overreach of federal authority,” said Juanita Molina, executive director of Tucson-based human rights group Border Action Network.

“Humanitarian aid is vital to the survival of migrants crossing the desert,” she added.

US Border Patrol referred questions to the US Attorney’s Office. It did not respond to a request for comment.

Prosecutors are expected to argue Warren went beyond humanitarian aid.

Jury selection for the trial in US District Court, Tucson, begins on Wednesday morning, and opening statement are expected later in the day.