A year after settling the biggest-ever strike in US higher education, the University of California has been reclassifying thousands of affected workers in ways that sharply cut their pay, raising the pressure for more job action, union leaders warned.

After months of trying to talk with system leaders about the danger of avoiding compliance with the contract, hundreds of graduate student workers rallied on the flagship campus at Berkeley and visited deans to personally push them for a resolution.

While the?resumption of a strike?wasn¡¯t a first option, the turnout suggested a growing level of discontent among the graduate students, whose teaching and research work provided a critical supplement to faculty, said Ruby Kharod, a graduate student in chemistry at the University of California, Berkeley.

The idea of a renewed walkout ¡°is still on the table¡±, Ms Kharod said. ¡°But I think the university would be quite silly to not resolve this internally, because the contract is already set and they should just be following it.¡±

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Last November¡¯s strike, involving about 48,000 academic workers, lasted for six weeks. The walkout produced a new three-year contract that promised to raise starting pay, from about $22,000 (?18,000) to $35,500 for graduate student researchers, and from about $23,000 to $34,000 for teaching assistants, along with improved benefits in areas that include healthcare, childcare and transportation.

But the California system had been avoiding those higher pay levels in hundreds of cases by systematically reclassifying workers, especially those in their first years, Ms Kharod and other union officials said.

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Examples, Ms Kharod said, included graduate students involved in teaching, who were previously paid as associate instructors,?but were now being paid as teaching assistants. In her department, she said, that amounted to an annual salary cut of about $2,000.

Graduate student researchers paid on fellowships had also been reclassified to lower pay rates, according to the union representing the graduate students. Overall, the union said, the tactic had affected about 1,500 graduate students at Berkeley and thousands more across the system, costing them ¡°hundreds of dollars each month¡±.

System officials said that the university was ¡°aware of concerns expressed regarding pay and job titles¡± and was working to resolve them, but declined to say whether it was intentionally reclassifying workers to hold down salaries.

¡°We continue to work through contract implementation matters in good faith, within the terms of the contract and within the law,¡± the university said.

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Part of the problem, union leaders said, was that the system accepted the contract without having identified how the additional money would be paid. For those workers involved in research, their salaries often come from already-fixed grant amounts?and, while many departments used their endowments to bolster low salaries for graduate students, the contract wasn¡¯t clear about how those amounts would be counted going forward.

The chair of the Berkeley Faculty Association, James Vernon, a professor of history, said he had sympathy for graduate students, watching them struggle to get answers. ¡°It¡¯s really important that the university finds a systemic solution to honouring the contract, rather than leaving it to individual faculty or individual departments to find ways of honouring it,¡± Professor Vernon said.

The dispute comes as?labour actions and threats?persist on campuses across the US. One of the biggest is also in California, where faculty in the 23-campus, 450,000-student California State University system have authorised a strike.

paul.basken@timeshighereducation.com