The event -- scheduled for Aug. 24 on the steps in front of the Lincoln Memorial where King delivered the landmark speech Aug. 28, 1963 -- comes amid "a climate that is threatening too much of what was achieved 50 years ago," the Rev. Al Sharpton and Martin Luther King II said in a statement.
"This is not just a nostalgia visit, that this is not a commemoration but a continuation and a call to action," Sharpton said.
U.S. Rep. John Lewis, D-Ga. -- the only surviving speaker from the 1963 event -- is among the more than a dozen leaders from Congress, clergy, the civil rights and women's movements, unions and immigration advocates scheduled to appear.
More than 40 groups are participating in the "National Action to Realize the Dream" march and rally.