One group left from Chicago and another from Des Plaines, Ill., Sunday morning.
Mack Julion, president of the Letter Carriers Local Branch No. 11, called the rally "awesome."
He said he was impressed by the turnout of letter carriers not only from the Chicago area but Wisconsin and Minnesota as well.
"The same faction that is coming against workers there in Wisconsin are the same faction that's coming against workers in Ohio, in Indiana. They're the same faction that wants to turn back the clock on labor laws and would like to see the postal service privatized," Julion said.
Hundreds of people rallied in Madison, Wis., in support of Gov. Scott Walker.
It was organized by the national conservative group Americans for Prosperity.