In reaction to President Trump’s policy of separating families at the border, students and labor leaders at the University of California are urging UC President Janet Napolitano to sever contracts with dozens of companies doing business with the federal Immigration and Customs Enforcement agency.

UC labor leaders say they’ve found 25 companies — from uniform suppliers to weapons manufacturers — that do hundreds of millions of dollars of business with the university, and with ICE.

“We want UC to remove resources that are critical to ICE’s enforcement of zero tolerance and take a stand for” immigrants and people of color, said John de los Angeles, spokesman for the American Federation of State, County and Municipal Employees, AFSCME Local 3299, which represents thousands of workers across UC campuses and medical centers.

UC spent at least $281 million on contractors who also do business with ICE, according to an AFSCME report on UC vendor contracts from 2011 to 2015, the last year of contracts available online.

The weapons manufacturer on the list is General Dynamics, whose subsidiary, General Dynamics Ordnance and Tactical Systems, provides ICE with its ammunition, the union says.

The company doesn’t sell ammunition to UC. It administers writing tests for 16,000 freshmen and applicants through a different subsidiary, General Dynamics Information Technology.

General Dynamics Information Technology also “employs staff who support and facilitate the forced separation of children and parents seeking asylum at the U.S. border,” says a June letter to Napolitano from the executive board of the UC chapter of the American Federation of Teachers, asking her to cancel UC’s contract with the company, worth about $2.6 million.

Napolitano declined the union’s request.

As secretary of homeland security under President Barack Obama, Napolitano presided over what was then a record number of deportations, primarily focused on people with a criminal record. She is also the author of DACA — Deferred Action for Childhood Arrivals — a federal law that in 2012 began allowing undocumented immigrants who arrived in the United States as children to study and work without threat of deportation, and which Trump has tried to dismantle.

Napolitano told the faculty union that she has publicly opposed the Trump administration’s “zero tolerance policy separating immigrant children from their parents, which I find to be cruel and morally unjustified.”

Even so, she said, General Dynamics Information Technology “has stated publicly that it has no role in the family separation policy, and plays no role in the construction or operation of detention facilities.”

Mia McIver, who teaches writing at UCLA and is president of the UC teachers federation, said Napolitano is making a mistake. She pointed to the website of General Dynamics Information Techology, in which it describes its connection to the miliary, though not to ICE.

Another business on the union’s list is Deloitte, a business consultant that UC paid nearly $72 million in the five years examined by AFSCME.

UC also spent $64 million with Aramark, a uniform and laundry service, in that time, and $32 million with ABA, which leases parking facilities. Both also do business with ICE.

A spokeswoman for Napolitano said the UC president was on vacation and could not be reached for comment Friday.

Napolitano’s unwillingness, so far, to divest from the companies irritated AFSCME President Kathryn Lybarger, who issued a statement asking whether Napolitano will “stand up to Trump’s deportation force, or enrich it? This is a fundamental question of leadership and morality, and she can’t have it both ways.”

Stephanie Luna, an incoming junior at UC Berkeley majoring in ethnic studies, is one of several students who spoke at last month’s regents meeting and asked the UC governing board to divest from the companies.

“As the daughter of immigrants, and having known people going through these situations, it’s devastating,” Luna, whose parents are from Mexico, told The Chronicle on Friday.

“I don’t see how universities can be doing business with companies and contractors that are enabling this,” Luna said. “Especially when President Napolitano has stated that the university is on the side of the students and their families.”

Nanette Asimov is a San Francisco Chronicle staff writer. Email: nasimov@sfchronicle.com Twitter: @NanetteAsimov