The El Chaparral crossing from Tijuana, Mexico, into the US is the crossroads of the world. Sisters from El Salvador plait one another’s hair; men from Cameroon await an asylum hearing on the far side. Iranians play dice; a father from Brazil buys his child a taco from a street stand with carefully counted coins.

Groups of young Americans also converge carrying armfuls of papers. They are also migrants of a sort: they have come from all over the US to volunteer for a remarkable organisation called Al Otro Lado – To the Other Side.

As the Trump administration turns the screw on migrants – refusing to accommodate those awaiting asylum interviews as law requires – these people, their counsel and sustenance to those in flight and need, are a counterforce against cruelty.

Nicole Ramos, the director of the group’s border rights project, defines Al Otro Lado’s job as “work that never ends”. And the principle of that work is “to get the courts and federal law enforcement to follow federal law. To stop the people whose role is to uphold the law from routinely breaking it.”

Asylum seekers wait to be transported to the US, at El Chaparral crossing port at the US-Mexico border, in Tijuana, Mexico. Photograph: Guillermo Arias/AFP/Getty Images

Ramos exudes tireless, effervescent purpose. She wears a ring made of bullet casing, with the round made of obsidian. “I came here to apply what I knew about the broken system,” she says.

Ramos arrived in Tijuana to volunteer at its migrant shelter, but became outraged by the difficulties asylum seekers faced in presenting themselves to US authorities. She teamed up with two immigration attorneys working in southern California: Nora Phillips and Erika Pinheiro, who founded Al Otro Lado in 2011.

“In the last month, we’ve counselled over 2,000 migrants. This is the new normal,” she says. “People are going to keep coming. We are barely stemming the tide, and so many people are hurting so much”.

The first step for an asylum-seeker is to present themselves at a port of entry like this one, and wait in detention by US Immigration and Customs Enforcement (Ice) for a “credible fear interview”, after which one may or may not get a court hearing. After sending refugee Jews back to die in Nazi Germany, the US signed the 1939 Montevideo Treaty on asylum, under which any foreign national appearing at the border and expressing fear of violence at home must be granted an interview with an asylum officer.

US Customs and Border Protection (CBP) has no statutory authority to the contrary, but refugees are now kept waiting for weeks or months.

In December the new Mexican government of Ándres Manuel López Obrador accepted Trump’s new “remain in Mexico” policy, under which asylum seekers are sent back to Mexico after their interview, until scheduled to appear before a judge – a process that can take up to four years. Last week, the US unilaterally returned a number of asylum seekers through the San Ysidro crossing.

As they did so, two shocking episodes brought Al Otro Lado’s work into disturbing limelight. On 29 January Pinherio, an American citizen, was stopped crossing into Tijuana, inexplicably detained two hours and returned to the US. Papers proving that her infant son was Mexican were of no consequence.

Two days later, Phillips was detained while travelling with her family into Guadalajara airport; she was held seven hours with her daughter, denied water and medicines, and deported back to the US.

It remains unclear which government blacklisted their passports. “I think this is retaliation,” said Phillips, “I think it’s that we’re pointing out gross, flagrant human rights violations being committed by the US government, and they don’t like that.”

Al Otro Lado works on both sides of the border, representing both detained and non-detained immigrants in US court proceedings and educating migrants of their rights under US law.

Asylum seekers line up to register with Mexican Immigration officials at a shelter in Piedras Negras, Mexico, 5 February 2019. Photograph: Jerry Lara/AP

There’s no attempt to feed migrants’ dreams or delusions, said Ramos: “We’d be violating our own ethos if we didn’t warn people and explain the grim realities of detention. I tell them: ‘The US government will try to break you, and you have to be stronger than them.’”

Al Otro Lado’s Tijuana premises occupy three storeys of Enclave Caracol, a food co-op and free vegan cafe, bike workshop and music venue.

Outside is charismatic, scary Tijuana; the second largest city on the Americas’ Pacific coast after Los Angeles and Mexico’s homicide capital. But as lunchtime approaches, Al Otro Lado’s main space doubles up as a free canteen, then seminar room for “Know Your Rights” sessions – Spanish for some three-score people, plus English and French/Haitian Creole for smaller groups upstairs.

Two legal assistants running these sessions were themselves deported. Pricila Rivas was “separated from my parents after living all my life in the USA, deported to a place I didn’t know, where not even knowing Spanish makes me Mexican”; and Rigo Martínez, deported “by myself, 10 years ago from California, where all my family lives”. It helps, says Pricila, “that we went through what [the migrants] are going through, the other way round. It was so scary being deported without the information we needed.”

Finally, Ramos finds time to feed herself, and we adjourn to a taqueria next door. The US authorities “despise us for informing people”, she says. “We tell migrants that once they get to the port of entry, everything that happens is potential ground for litigation, and the authorities don’t like people knowing their rights.

“People on the other side say we’re fake lawyers, troublemakers. They call us radicals. Well, if following the law is radical, let me be radical.”

Into the office comes Jess Fuller, responsible for technology and administrative support, with a laptop containing details of 1,400 migrant consultations she has processed over two months. “So many people come in,” she says, “it’s easy for their cases to fall through the cracks.”

In an interview before she was turned back from Mexico on 29 January, Pinheiro warned that the Trump administration’s policies are exposing asylum seekers to very real dangers: “We’ve had so many disappearances, reports of people who’ve either been disappeared by organised crime or forced to work for them.”

A migrant family waits before being transported by Mexican authorities to the San Ysidro port of entry to begin the process of applying for asylum in the US. Photograph: Gregory Bull/AP

“Gangs and death squads follow them,” adds Ramos, “chasing them through Mexico, or through affiliated gangs here.”

Pinheiro, the daughter of Portuguese immigrants, is a specialist in child and immigrant detention in Los Angeles.

“I’ve worked many years in detention facilities in the US – immigrant detention for adults and kids, county jails in LA – and it’s been very hard. But what we had until now was the US government following the law, more or less. People were in danger, but there were rules.

“Now it’s very different: we have another level of desperation among those applying, and we just don’t know what the rules are. We keep following the law and statutes, but the government is not following the law. I’ve been practising law a good while, and I’ve never seen it so routinely broken by those who make it.

“There are no more norms,” continues Pinheiro, “what the government does is illegal, but CBP is an agency that operates with almost total impunity. How do I do my job if the US government is breaking the law?”