Unison could scupper the pay deal for all university staff as the union heads for make-or-break talks at its annual conference on Sunday.
The deal, which could see some lecturers' salaries rise by 5.1 per cent and will give manual workers the biggest pay increase ever, is conditional. It will collapse unless all eight higher education unions accept a package that includes the pay offer and a major reform of the national pay bargaining machinery.
Unison is the only higher education union that has put the offer to a ballot of its members without an executive recommendation to accept it.
The deal is expected to dominate discussions at the Brighton conference of Unison's higher education service group.
Unison is relatively happy with the pay side of the deal, which offers rises of more than 6 per cent for the lowest paid manual workers.
The union's concern is over new arrangements for national pay bargaining. These will sweep away the eight separate bargaining systems and create a single Joint Negotiating Committee on pay, with a single pay spine for all staff and a common pay anniversary date, August 1, for all.
The JNC will be split into two subcommittees. One will bring the academic unions together round a single new negotiating subcommittee for academic staff. The other will cover professional, technical, administrative, and ancillary staff.
Unison has opposed any split between academic and non-academic staff in the JNC and has campaigned heavily for a single table for all.
Even more disappointing for Unison, the subcommittee split has allowed the 20 per cent of the Association of University Teachers' members who are "academic-related" to join the academic sub-committee.
Its executive has agreed that it cannot recommend the package to members.
This week, Unison education services national officer Christine Lewis said that she believed the prospect of the best pay increase ever for some members would mean Unison would vote to accept the deal.
She said: "Unison is a broad church, and it is clear that the composition of the subcommittees is more dear to some members than others. If the lowest paid in new universities can see their best ever pay deal, they may not be so worried about the future bargaining structures."
Unison's ballot result is due on June 21, four days before a final meeting between unions and employers.
Lecturers' union Natfhe has already accepted the deal, with more than 80 per cent of members in favour.
AUT members are expected to accept the offer by a significant margin in a ballot due to be confirmed today.
The Transport and General Workers' Union is also predicting a resounding "yes" vote for a rise that would give some members 6-7 per cent extra.