New York University’s president, John Sexton, has been surprised by the outrage expressed by many students and faculty members at the university’s tentative decision to break off relations with its graduate student union, according to some NYU professors.

Mr. Sexton has been using the normally quiet summer months to deal with complaints from those demanding that NYU instead renegotiate its contract with the union for its graduate assistants, who teach a large number of the school’s courses.

Famous on campus for the hugs he extends to visitors, Mr. Sexton has maintained generally good relations with the university community since becoming president in May 2002. The ill feeling over the labor decision has been jolting, campus observers said, and culminated with a hostile town hall meeting last month at which some students and faculty members jeered at the president.

NYU, the only private university in America with unionized graduate students, said in June that it would no longer use the United Auto Workers as an intermediary with its students and blamed the union for filing grievances that the university said interfered with academic judgments. It said it would allow 30 days for the university community to react before a final decision was made – a period that ended two weeks ago. A decision is expected by the end of this week.

The UAW represents about 1,000 NYU teaching and research assistants, whose contract with the university expires at the end of the month. That contract, which NYU ratified after the labor relations board ruled against the administration, guaranteed annual stipend increases of $1,000 a year. NYU has pledged to continue the $1,000 increases for the next three years, pushing minimum annual stipends for doctoral students to $21,000.

The university was taking advantage of a ruling a year earlier in a case involving Brown University, in which the National Labor Relations Board held that graduate assistants are primarily not employees but students. The board in that decision reversed its November 2000 ruling in favor of unionizing graduate students. Union supporters have said graduate students are primarily workers who are vulnerable to exploitation.

Mr. Sexton played host to a town hall meeting on July 12 to allow members of the university community to discuss the issue. He faced a largely hostile audience composed overwhelmingly of supporters of union recognition, some of those who were present said.

“It was probably quite jarring,” a philosopher, Paul Boghossian, who opposes the graduate students’ union, said. Mr. Boghossian is one of about 145 faculty members who signed a letter to Mr. Sexton urging him not to waver on his ruling against the union.

A professor of American studies, Andrew Ross, said Mr. Sexton was “visibly shaken” by the town-hall meeting. Mr. Ross said graduate student assistants this fall semester will have no choice but to go on strike.

Officials of the UAW said they are leaving open the possibility of some form of job action, which could be immensely disruptive for the university. A strike by graduate students at Columbia at the end of the spring 2004 semester truncated dozens of courses and led to the cancellation of exams and term papers.

Mr. Ross said a petition calling on NYU to preserve its graduate student union has collected more than 200 signatures of faculty members.

A spokesman for NYU, John Beckman, said he found the town-hall meeting “disappointing.”

He said, “It was characterized by a lot of sloganeering and a lot of posturing.”