Teaching assistants at Columbia and Yale Universities walked picket lines rather than lead classes Monday -- and plan to continue doing so for the rest of the week.

Union organizers pointed to large rallies and pledges of support from politicians to suggest that the week-long walkout is off to a good start. Unions at the two universities are pushing for recognition. Both institutions say that the TA's should be considered primarily students, not employees eligible for collective bargaining. By coordinating their action, the unions hope to gain more attention for their cause. The teaching assistants say that they are underpaid, lack sufficient benefits, and need better protection of their rights.

"The pickets and enthusiasm are really strong," said Felicity Palmer, a graduate student in English at Columbia who did not teach her scheduled class Monday. Palmer is a volunteer organizer for Graduate Student Employees United, a United Auto Workers chapter at the university.

Palmer said that the union did not have estimates of how many classes had been called off, but she said she believed it was a large number.

Rachel Sulkes, a spokeswoman for the Graduate Employees and Students Organization at Yale, said Monday evening that about half of all teaching assistants were honoring the picket lines, either by calling off class or in a few cases moving instruction off campus. She said about 450 courses were affected.

Both Yale and Columbia continue to defend their policy of not recognizing graduate student unions, and they were bolstered by a National Labor Relations Board ruling last year that they don't have to. And both universities said that they thought the impact of the strike had been minimal so far. A Columbia spokeswoman said that the campus looked normal, with students going to classes and enjoying the arrival of spring.

Thomas Conroy, a spokesman for Yale, said that he believed undergraduate education "has been minimally affected" by the strike, which he said appeared designed "not to disrupt education, but to draw public attention."

Conroy said that classes are meeting as scheduled, but that some professors have merged discussion sections into larger "town meeting" style classes or recruited others to cover for striking teaching assistants. He also noted that 70 percent of undergraduate courses don't involve TA's.

While the strikes at both universities have attracted undergraduate support, at a time that labor issues are attracting widespread student interest, others have been critical. An editorial in The Yale Daily News backed the university's position on the status of graduate students.

"Graduate students come to Yale as students, not as workers, and while here, their services as workers, no matter how valuable, are still secondary to their role as students," the editorial said. It added that strikes by graduate students -- this is the 6th in 15 years at Yale -- don't accomplish much since the university's position is unchanged.

Sulkes, the spokeswoman for the Yale union, rejected that idea. She said that even though the university has refused to recognize the union, it has improved conditions for graduate students -- generally at times of heightened union activity. "By doing this with Columbia, we are showing that the movement is growing, and that's going to have an impact," she said. "This issue is not going away."