New York police used batons and pepper spray against hundreds of demonstrators trying to stage a late night march.
At least 28 people were arrested, including one person who was booked for assault. There was no word of any serious injuries.
The confrontation capped a day in which union members joined the marches and rallies - the largest since Occupy Wall Street activists began holding protests and campouts targeting corporate America.
The protests started Sept. 17 with a few dozen demonstrators who tried to pitch tents in front of the New York Stock Exchange. Since then, hundreds have set up camp nearby in Zuccotti Park and have become increasingly organized, lining up medical aid and legal help and printing their own newspaper.
The protesters are demanding higher taxes for the wealthy and job incentives for the middle class.
Labor leaders say they will continue to support the protests, both with manpower and donations of goods and services.
The Associated Press contributed to this report.