Then late last year, administrators at the college delivered letters to dozens of the longtime employees asking them to show proof of legal residency, saying that an internal review had turned up problems in their files. Seventeen workers could not produce documents showing that they were legally able to work in the United States. So on Dec. 2, they lost their jobs. Now, the campus is deep into a consuming debate over what it means to be a college with liberal ideals, with some students, faculty and alumni accusing the administration and the board of directors of betraying the college’s ideals. The renewed discussion over immigration and low-wage workers has animated class discussions, late-night dorm conversations and furious back and forth on alumni e-mail lists. Some alumni are now refusing to donate to the college, while some students are considering discouraging prospective freshmen from enrolling. For the last two years, many of the dining hall workers had been organizing to form a union, but the efforts stalled amid negotiations with the administration. Many on campus believe that the administration began looking into the employees’ work authorizations as a way to thwart the union effort, an accusation the college president, David W. Oxtoby, has repeatedly denied. But that has done little to quell questions and anger among the fired workers and many who support their efforts to unionize. “We were here for a very long time and there was never a complaint,” said Christian Torres, 25, a cook who had worked at the college for six years. “But now all of the sudden we were suspect, and they didn’t want us to work here anymore.” Mr. Torres, who still greets dozens of people on campus by first name, had been one of the primary leaders of the effort to create a union until he lost his job in December. Dr. Oxtoby said the board of trustees received a “specific, credible complaint” from an employee in early 2011 about the college’s hiring policies and moved to investigate the accusations. For months, officials said, lawyers from the law firm Sidley Austin combed through the university’s records and met with administrators. By the time the investigation was complete, the law firm had identified deficiencies in the files of 84 employees, including dining hall and maintenance workers as well as professors and students working for the college. Each employee received the same letter asking for documents to re-verify their work status. Of the 17 employees who ultimately lost their jobs, 16 were dining hall workers. Dr. Oxtoby said that when he heard the results, he “knew immediately this would be an explosive issue.” “This is a very sensitive issue especially in Southern California, and many of our students and faculty are immigrants themselves or are descendants of immigrants,” he said. Still, he said, he had no doubt that the workers would need to leave the college. “The law is very unforgiving, and unfortunately we have to obey the law even though it really hurt the community.” The idea that the college had mounted the effort to stop the union drive was the opposite of the truth, he said. “We’ve been trying to improve the relationship with workers for some time, and this has been a big setback,” Dr. Oxtoby said. “Rationally, it would have not made strategic sense.” Dr. Oxtoby and the college’s trustees repeatedly said there was no choice but to fire the workers. In a letter from the law firm, lawyers for the college said the college would have left itself open to investigation and punishment from federal immigration authorities had it not fully examined the employment files. Pomona is part of a consortium of seven colleges whose campuses intertwine here. In December, a day before the Pomona workers were fired, a human resources officer at Scripps College, another member of the consortium, called seven employees there asking them to complete a new work authorization form.