Witnesses told CNN crowds at the "Occupy Wall Street" rally Wednesday seemed to be the largest since the protests began nearly three weeks ago and that the movement was growing, thanks to social media Web sites.
New York police said 28 people were arrested on a number of charges, including one for allegedly assaulting a police officer.
Similar protests -- although not as large -- have popped up elsewhere in the United States, such as Boston, Seattle, Hartford, Conn., and Savannah, Ga. Demonstrations were expected to occur in Washington and Tampa, Fla., on Thursday.
Several unions announced their support earlier this week.
"These young people on Wall Street are giving voice to many of the problems that working people in America have been confronting over the last several years," said Larry Hanley, of the Amalgamated Transit Union, which has 20,000 members in the New York area.
"These young people are speaking for the vast majority of Americans who are frustrated by the bankers and brokers who have profited on the backs of hard-working people," Hanley added in a statement. "While we battle it out day after day, month after month, the millionaires and billionaires on Wall Street sit by -- untouched -- and lecture us on the level of our sacrifice."