Students could be hit by strike action at exam time as a universities union warned of more walkouts in a pensions row.
The University and College Union (UCU) announced a further 14 days of strikes designed to target the examination period between April and June, if there is no resolution in ongoing talks.
Thursday saw the ninth day of strike action since February 22.
Talks are continuing between the union and Universities UK (UUK) through the conciliation service Acas.
UCU said there could be strikes at 65 institutions, and that the union would gather information to see when the next wave of strikes would be most effective at different universities.
But UUK, which represents the universities, said it was disappointed by the continued industrial action and described current talks as serious and constructive.
The dispute centres on proposals put forward by UUK in January which would see the Universities Superannuation Scheme (USS) move from a "defined benefit" scheme, which gives workers a guaranteed income in their retirement, to become a "defined contribution" scheme, in which pensions are subject to fluctuations in the stock market.
UUK maintains that the pension scheme has a deficit of more than £6 billion that cannot be ignored.
UCU argues that the current proposals would leave a typical lecturer almost £10,000 a year worse off in retirement.
Ahead of the talks, UUK warned that failure to secure a deal would cost universities and their staff £1 billion a year.
Announcing the next potential wave of strikes, UCU general secretary Sally Hunt said: "I want to stress that I consider all this a necessary precaution against the failure of talks to deliver an acceptable settlement.
"The union would prefer dialogue and I have given my personal commitment to Acas that UCU is serious about reaching an agreement.
"However, if talks fail, we are prepared to carry out the action in defence of our pensions.'
A UUK spokeswoman said: "UUK are disappointed that UCU are preparing for additional industrial action that could further disrupt students' education."
"Both sides are currently engaged in serious and constructive talks at Acas.
"We are committed to seeking a viable, affordable and mutually acceptable solution to the current challenges facing USS pensions."
"UUK has again restated its request to the union that industrial action is suspended while talks at Acas continue. As part of any alternative proposal, we will expect that industrial action is suspended while UUK consults with all employers."
Talks are due to resume on Friday.