More than 60 universities have formally challenged the University and College Union's ballot for industrial action on the ground of inaccuracy, according to employers.
Before the ballot, which opened on 1 May, the union was required to inform institutions of the numbers of staff taking part, their categories and locations.
However, Jocelyn Prudence, chief executive of the Universities and Colleges Employers Association, said the UCU had included postgraduate students and cited non-existent departments.
She said: "In one case, 300 staff in a small college have been balloted directly, and a university has been notified that these staff have been included in its ballot. The scale of inaccuracy is very significant and could render the ballot unlawful."
A UCU spokesman responded: "We are happy we have met our statutory obligations, but we don't intend to have a discussion in the press about it."
The UCU called the ballot over pay and its demands for a national redundancy-avoidance policy. It wants a pay rise of at least 8 per cent for 2009-10, while employers have offered 0.3 per cent.
All campus unions, backed by the National Union of Students, unveiled a draft redundancy-avoidance agreement this week, under which institutions would form redundancy-avoidance committees, ring-fence vacant posts and set up a register of staff in need of redeployment.
Universities are asked to set aside cash for training in transferable skills, including part funding of higher education study, and to collaborate with other regional institutions to extend redeployment opportunities.
The unions also want at least 30 days added to the statutory notification period.
In a joint statement, the unions say Ucea had raised "the spectre of mass redundancies" across the sector during pay negotiations. They add: "There should be nothing in principle to stop the higher education sector from coming together to provide reassurances on seeking to avoid job cuts rather than their current position - hiding behind claims of institutional autonomy."
But Ms Prudence said: "The UCU wants an 8 per cent rise and a no-redundancy agreement. I question how well those two things sit together."