Graduate students at New York University say they will go on “strike,” declining their instructional duties starting November 9 to protest the administration’s refusal to recognize their union.

Local 2110 of the United Auto Workers, which represented NYU’s teaching and research assistants under a contract that expired two months ago, said the student strike would last as long as NYU refuses to negotiate another contract.

NYU’s president, John Sexton, has said the university won’t change its mind and that faculty members and officials will do what they can to minimize disruptions for undergraduates who pay $31,690 in annual tuition. The university stands to lose a portion of its exam and term-paper graders, as well as teaching assistants and laboratory instructors. Graduate student strikers may also include stand-alone teachers, mostly in foreign language courses.

Unless NYU can fill the positions quickly, exams could be canceled or postponed, assignment could go unmarked, and students may receive grades later than normal. Some faculty members have indicated they will move their classes to off-campus locations as a symbolic show of support for the graduate students on strike.

NYU officials have reassured undergraduates that the school has a contingency plan in place to deal with such a walkout and predict that most of its graduate assistants with teaching duties will not go on strike. About 1,000 graduate students are assigned to teaching and research assistant positions at any one time, according to NYU.

The university has also threatened graduate students with unspecified consequences for failing to meet their instructional responsibilities. “The university has been doing the appropriate planning,” a spokesman for NYU, John Beckman, said, while refusing to go into details about NYU’s strategy.

For about three years, NYU was the only private university with unionized graduate students. After the National Labor Relations Board in 2004 overturned its 2000 ruling that forced NYU to recognize the union, NYU decided to cut ties. NYU accused the union of violating the previous contract by filing frivolous grievances that challenged the university’s power to choose who teaches which courses.

Graduate students in favor of unionization argue that a contract is a safeguard against exploitation, and union officials said they would withdraw their grievances. NYU pays doctoral students a minimum annual stipend of $19,000, which will increase by $2,000 over the next two years. That amount is one of the highest rates among competing universities. Support for a strike among graduate students varies among departments. Students most active in the union appear to be concentrated in the humanities and social science disciplines, while graduate students in the hard sciences and in the business school are far less likely to stop teaching.

For guidance, NYU officials could look to the example set by Columbia University, where graduate students staged brief strikes in 2004 and 2005 for similar reasons. Last year, Columbia’s provost, Alan Brinkley, distributed a letter to deans that suggested ways the university could minimize disruptions.

The letter, obtained by the Nation magazine, proposed replacing graduate student teachers with adjuncts, combining classes, and hiring new part-time faculty members. Mr. Brinkley said the university could eliminate stipends and require strikers to teach an extra semester to fulfill requirements. The impact of the April strike was ultimately minor, and most of the recommendations were not implemented.