Support for a one-day strike by higher education lecturers across the UK has been "solid", unions claim.
The AUT said the strike had been a success
The AUT said many students had also shown their backing for the strike by not attending lectures and classes.
But university employers said early indications were that the action had a "minimal impact", and that many students had voiced concerns.
Tuesday's strike by Natfhe and AUT members is due to be followed by a boycott of assessments and appraisals.
Sally Hunt, general secretary of the AUT, said the industrial action was "absolutely solid".
"On campuses and in the areas outside each and every university entrance there are solid picket lines and no-one is going in," she said.
Ms Hunt said employers had spent six months refusing to negotiate and she was "beginning to question their integrity".
"All we're asking for is that the commitment they have given to their staff is honoured.
"The academics on strike are good, reasonable people who have been forced into an unreasonable action."
Natfhe, which mainly represents members at newer universities, said teaching had been cancelled at a number of institutions.
Its head of universities, Roger Kline, said employers had been sent a clear message to make a fair pay offer.
The unions say their case is based on years of low pay increases - highlighted, they point out, by the prime minister among others, and used as a prominent argument to get through legislation on variable tuition fees.
The two unions, whose members have voted for a merger, say universities are getting £3.4bn extra from top-up fees and other funding.
Roger Kline told BBC Radio Five Live that lecturers' salaries had fallen in real terms over the past 20 years.
"The average pay is for about £30,000 to £35,000 for almost all of our members. They could get much more earning in the private sector."
The Universities and Colleges Employers' Association says the unions are embarking on industrial action even before this year's pay round has begun and branded their pay claim "unrealistic".
UCEA says that between 2001 and 2005, academics' earnings increased by 20.3%.
Its chief executive, Jocelyn Prudence, said: "Early indications from universities and higher education colleges show that the patchy nature of today's strike action is creating minimal impact.
"In many institutions there has been no action whatsoever and students have crossed picket lines, with many voicing their concerns over the unions' premature strike action - in particular plans to boycott assessment and marking."
UCEA says well over one third of the sector's new income from fees in 2006-07 is expected to be spent on staff pay and conditions.
But this will include extra staff, higher pension contributions and the cost of pay modernisation, as well as pay increases from this August.
The unions said members had reacted with "fury" to employers' claims that the average salary was more than £40,000.
That applied in only 10 out of 170 institutions, they said, and the overall average was less than £36,000.
The employers claim figures from the Office for National Statistics on hours and earnings show academics earned an average of £40,657 in 2004-05, compared with averages of £28,210 for all employees and £36,894 for all professional staff.
The unions said the most recent figures from the Higher Education Statistics Agency - for the previous year - showed that in only 10 out of 170 institutions did academic staff earn an average of more than £40,000.
The overall average, they said, was actually £35,773, and UCEA's figures ignored thousands of staff who were on fixed term or hourly contracts with lower pay rates.