The scuffle happened as students stormed the Jubilee building in Brighton to shout "join the strike" at others sitting in a psychology lecture.
"We are striking reluctantly with a heavy heart", history lecturer Mike Berlin said on a picket line at Birkbeck University.
Universities UK (UUK) maintains that the pension scheme has a deficit of more than £6 billion that can not be ignored, and that it has met union officials more than 35 times to discuss reforms, The Press Association reports.
A group of protesters gained access to the Universities UK (UUK) headquarters in central London, where they staged a sit-in.
The National University of Students (NUS) said it supports UCU members' decision to strike, and encouraged NUS members to support their lecturers.
Employers argue the pension scheme is £6 billion in deficit, while the union says the proposals would leave a typical lecturer nearly £10,000 a year worse off in retirement.
Taking a stand, the UCU issued a notice that it was to take industrial action - spread across more than 60 universities, including Oxford and Cambridge - over the course of the next month, and possibly more months after that if demands are not met.
As a result of the changes, a person who starts work today could lose approximate £10,000 a year from their pension.
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Sam Gyimah, a Conservative Party MP and Minister for Universities, called on both sides to negotiate without preconditions. Banners reading "Support our Staff" and 'Strike to Win!' were displayed outside the faculty building along with smoke sparklers created to attract attention. Several hundred students engaged in chants led by CUSU President Daisy Eyre, including, "They say marketise, we say organise", and, "Students and workers, unite and fight".
Staff at universities founded since 1992 are members of the Teachers' Pension Scheme, so aren't affected by the changes.
A spokesman said: "UUK remains at the negotiating table, but so far UCU has refused to engage on how best to address the funding challenges facing USS".
As a result, some UCU members at 64 unis have chose to strike for 14 days over the next four weeks.
The union said there were "a number of misleading claims" about the planned changes to the pension scheme, which had been "affected by hard economic conditions".
Universities UK said it has met UCU over 35 times in the a year ago to discuss reforms.
"The cost of future pensions has risen by one-third in the last three years, and the scheme has a deficit of 6.1 billion (pounds), which, by law, must be reduced", Universities UK said.
"I am deeply concerned about the impact this strike will have on students who deserve to receive the education that they are paying for", he said in a statement.
"If this round of strikes fails, there is a possibility of further strike action which could affect our exams later on in the year, it could affect marking, and, ultimately, whether we can graduate or not".