For the first time in nearly 20 years, faculty members at the University of Minnesota’s Twin Cities campus are calling for an election to form a union.

Organizers say they plan to file a formal petition Wednesday on behalf of some 2,500 full- and part-time instructors at the U’s largest campus.

If the vote goes their way, this would become one of the largest faculty unions in the country, according to the Service Employees International Union (SEIU), which is sponsoring the organizing effort.

The group, which began its organizing campaign in the summer of 2014, said it has collected enough signatures — 30 percent of the proposed membership — to trigger a union election, and that a vote could come in three or more months.

One of the goals is to improve job security and pay for more than 1,100 contingent faculty members who are not on the tenure track, said Naomi Scheman, a philosophy professor who helped lead the unionizing effort.

She said the increasing reliance on low-paid instructors “with no job security” is one of the alarming trends in higher education. “There need to be more tenure track positions, I think everybody agrees,” she said. “We need to stop this creeping reliance on contingent faculty.”

University officials declined to comment on the union drive, saying they had yet to see the petition. But Vice President Kathryn Brown issued a brief statement saying that the U “wants to continue working directly with faculty” on employment and other issues. “We believe the current governance structure gives faculty a strong voice and it will continue to be effective in the future.”

The campaign is part of a national movement to organize part-time instructors, sometimes known as adjuncts, on campuses around the country. Just last month, Hamline University in St. Paul announced its first tentative contract agreement with its adjunct union, which was formed in 2014. That same year, adjuncts voted down a union at the University of St. Thomas in St. Paul.

At the University of Minnesota, the proposed bargaining unit would include both tenured and nontenured faculty members on the Twin Cities campus, with exception of the law school, medical school and other health sciences.

Erin Trapp, who started teaching comparative literature at the U last fall, said that the union drive has been fueled by frustration over the treatment of contingent faculty like her. Trapp says it’s not just about the low pay and job insecurity, but the lack of professional opportunity for those in her ranks. Unlike tenured faculty, she noted, contingent instructors get no support for work beyond the classroom, such as mentoring students or pursuing their own research. “I can develop relationships with students but can’t serve in full capacity to advise them,” she said. “It’s hard to feel respected by other colleagues because of the division.”

Two of the university’s campuses, in Duluth and Crookston, already have faculty unions.

But the last faculty unionizing effort on the Twin Cities campus, in 1997, was rejected by 26 votes. At the time, many faculty members were up in arms about a proposal to weaken tenure protections, which ultimately was abandoned.

This time, says Scheman, her colleagues are worried about different kinds of threats to their profession. “The threat to tenure is not a threat to those of us who have it,” she said. “It’s a threat to those who are never going to get it.”

Before any vote is scheduled, the Minnesota Bureau of Mediation Services must determine if the petition is valid and who is eligible to vote, according to the union. So far, the SEIU has 38,000 members in other faculty unions, including Georgetown University, Tufts University and the California State University system.