The University and College Union insists that it will not allow an academic pay gap to open up between elite and less wealthy higher education institutions, and says universities will face "pain" if they move to local bargaining.
Sally Hunt, the UCU's general secretary, reaffirmed the union's commitment to national pay bargaining after the University of Exeter became the latest institution to reveal plans to pull out.
David Allen, the Exeter registrar and deputy chief executive, told staff that local negotiations would allow the university - one of the new AAB elite - to offer better pay deals, rather than being limited to what the "poorest" institutions could afford.
Ms Hunt said that while the UCU would defend national bargaining, it would be "putting a lot more resources into supporting local negotiators" to prepare for any moves to local bargaining.
"I don't think we should move away from national bargaining," she said. "But I'm absolutely clear that what this union will do is put the resources where it needs to in order to maintain parity between our members, because that is what our members pay us to do."
She added: "It isn't in the interests of any our members for there to be sliding scales of the very well-paid in one university and the poorly paid in another."
Ms Hunt said national bargaining was the "safest and fairest" option, both for staff and "for universities operating in an international and national market".
While a national pay spine is in place - covering staff from cleaners through to senior lecturers - some universities put their staff on higher pay points than colleagues at other institutions.
Ms Hunt said Exeter was a relatively high payer, proving that there is "already an awful lot of flexibility" within national bargaining. "There is flexibility for different levels of pay depending on which university you are in," she said.
"I'm not clear what, on top of that, the registrar (Mr Allen) was trying to drive at.
"From a university's point of view, that (local bargaining) is going to cost them. There is no change without some pain in this."
Ms Hunt said universities might experience "issues in terms of their reputation" if they move to local bargaining. Unions also argue that institutions face higher costs in training their local staff to negotiate.
Ms Hunt said that national pay bargaining should be judged not on recent low deals, but on the record over several years.
"I believe in national bargaining, I really do, if you look at how well it can work," she said, but added that the Universities and Colleges Employers Association "has refused to have any credible negotiations recently, on anything other than minimal pay negotiations".