A campaign to unionize adjunct professors has spread to a third St. Paul campus: the University of St. Thomas.

On Friday, President Julie Sullivan confirmed that adjunct, or part-time, instructors have filed a petition to hold a union election. The move comes just a month after adjuncts filed similar petitions at Macalester College and Hamline University.

The unionizing movement, organized by the Service Employees International Union (SEIU), has been fueled by concerns about low-pay and working conditions for adjunct instructors across the country.

In an open letter Friday, Sullivan said that St. Thomas, a Catholic university with some 10,000 students, "respects the right of our adjuncts to make a free choice about union representation." But she went on to express concerns about the unionizing effort.

"We believe the best way … is to work directly and cooperatively with adjunct faculty in each of our schools and colleges, rather than negotiating through collective bargaining," she wrote.

The university has 302 adjunct instructors who teach undergraduate courses, most of them part-time, according to spokesman Doug Hennes. The median pay is $4,300 a course, and they're generally not eligible for health insurance or other benefits, he said.

In her letter, Sullivan wrote that union contracts "tend to be rigid and inflexible," and that the university needs to work "with our adjuncts in a flexible way" to serve students.

Union advocates say that many adjuncts are hired at the last minute, to fill vacancies or teach classes as needed, and often don't know from semester to semester if they'll be invited back. They say colleges across the country are increasingly relying on low-paid adjuncts as a way to control costs.

Hennes said that St. Thomas has been working to address some of the concerns. This spring, he noted, the university decided to offer adjuncts free membership in its athletic and recreation complex for the first time. Officials also are studying the possibility of offering them health benefits, although they have made no promises, he said.

Last week, a group representing the St. Thomas adjuncts filed a formal petition with the National Labor Relations Board to hold a union election. If certified, the vote could be held in the next 30 to 45 days.

At Macalester and Hamline, voting is expected to begin soon, said Denise Welte, the organizing director for SEIU Local 284. Ballots will be mailed to adjunct instructors at each campus, and results will be available in about two weeks.

Maura Lerner • 612-673-7384