Oxford University has withdrawn the facilities it normally offers the Association of University Teachers to recruit new members following the union's decision to conduct a national ballot for industrial action over pay.
Sandra Nicholson, personnel officer at Oxford, informed the local union branch this month that "we feel we must withdraw the facilities offered to the AUT to assist with recruitment of new members" because of the dispute.
Her email also indicated that permission to set up recruitment stands on university premises, land or roads has been revoked, and that the university would not assist with recruitment mailings.
"We will review this situation once the dispute has been resolved," she added.
The AUT said it was "stunned" that Oxford was attempting to intimidate its members, claiming that they were "absolutely furious" about the pay and modernisation package.
It is the only union to reject the national framework negotiated with the University and Colleges Employers' Association. Its ballot on strike action closes on February 11, with the result announced the following day.
The AUT executive committee is urging members to vote yes. If the ballot is in favour of taking action, there will be an initial national strike, followed by regional strikes and actions such as boycotting assessment activity and call-out cover.
The union claims there is "huge enthusiasm" among members for a yes vote.
Sally Hunt, AUT general secretary, has written to Sir Colin Lucas, vice-chancellor of Oxford, and Sir Chris Patten, its chancellor, to protest against the ban on recruitment on the university's premises.
"I feel that your response is very heavy handed," she writes. "We hope your actions are not just a kneejerk reaction to the fact that reports indicate that members seem to be extremely enthusiastic about voting for strike action."
The union has also instructed its solicitors, Pattinson and Brewer, to write to the university. The firm's letter states: "The AUT is surprised that your university should contemplate such a step at all, but particularly that you should do so on the grounds that the AUT is, as it is of course fully entitled to do, holding a ballot for industrial action in connection with the current pay dispute."
The potential implications of the university's apparent change in attitude has disturbed the union, the solicitors write. They ask for an "unequivocal assurance" that Oxford will not threaten AUT members in any way.
It is understood that the university has not acted illegally, but any action taken against union representatives attempting to recruit members would be against the law.