A City University of New York professor is suing the union that represents CUNY faculty members, accusing it of overcharging nonmembers by making them pay for political activities unrelated to contract negotiations.

Brooklyn College professor David Seidemann, who is suing the Professional Staff Congress in federal district court in Brooklyn, claims that the union badly under calculates the amount of its “ideological expenditures.”

By state law, the CUNY union is allowed to collect a fee from faculty members who are not part of the union but are included as part of the bargaining unit. But nonmembers are not required to cover expenses for political activities that are not directly related to the faculty contract.

Mr. Seidemann, who is not a member, claims the union includes in its tally of contract-related expenditures money it spends on lobbying Albany to increase public school funding, hiring public relations firms, and public rallies, picket lines, and concerts.

Deborah Bell, executive director of the Professional Staff Congress, said the union is not overcharging nonmembers.

“I am quite confident that our figures are very solid,” Ms. Bell said. She said that union dues are 1.05% of a faculty member’s salary. Nonmembers are typically required to pay around 85% of that amount after political expenses are subtracted.

Mr. Seidemann said he recently received a $2,100 check from the union that covers his fees for the past three years. Ms. Bell would not comment on the payment.

Both Mr. Seidemann and the union have filed a motion for summary judgment and the court should be ruling on the case in the next few months.

Mr. Seidemann, a geology professor, has also formed a group composed of about nine other faculty members that accuses the CUNY union of wasting time and money on organizing activities like anti-war demonstrations and participating in international union conferences, while failing to negotiate a competitive contract.

“They are not focused on bread-and-butter issues but instead are focused on international solidarity issues and political causes,” Mr. Seidemann said. “As a result, I believe that the benefits are shrinking because of their lack of attention.”

Specifically, the newest dental plan, covered by the CUNY Welfare Fund that was agreed upon by the union and the CUNY administration, offers significantly fewer benefits than the old plan, according to Mr. Seidemann. The new plan, for example, does not cover orthodontic work, he said.