The Reverend Jesse Jackson and US Democratic presidential candidate Howard Dean have lent their support to efforts to resolve a strike over pay and pensions by workers at Yale University that coincided with Labor Day and the 40th anniversary of a historic civil rights march.
Some 4,000 secretaries, food service staff, maintenance staff and research assistants walked out as the university reopened for the academic year.
Management filled in to help arriving students.
Wealthy Yale, in working-class New Haven, Connecticut, has always had an uneasy relationship with the community.
Speaking on the anniversary of civil-rights leader Martin Luther King's "I have a dream" speech, Mr Jackson told strikers: "Surely, Dr King would rejoice at this sight. Yale has much to do about the brokenness of promises. It is on the back of those who were enslaved that this institution was built." Mr Jackson was among 14 people later arrested for blocking traffic at the campus.
Mr Dean supported efforts to negotiate a fair contract. Failing that, he called for binding arbitration as an alternative to striking.
The Federation of Hospital and University Employees said: "The university-wide strike highlights the key issues facing American workers this Labor Day: job security and retirement. Workers are increasingly finding their living standards under attack."
Yale president Richard Levin said the union was demanding unrealistic pension benefits.