"His attendance is an affront to the veterans of the civil rights movement," NAACP President Derrick Johnson said Tuesday.
The White House confirmed Trump's visit to Jackson on Tuesday at the invitation of Mississippi Gov. Phil Bryant, a Republican.
Asked about potential protesters at the event, White House Press Secretary Sarah Huckabee Sanders said, "that would be honestly very sad."
"This should be something that brings the country together," she said.
Trump and Lewis have had an acrimonious relationship for the better part of a year. Trump called Lewis' Atlanta-based 5th Congressional District "crime infested" and "in horrible shape" after Lewis, a high-profile Hillary Clinton supporter, said he didn't see Trump as a "legitimate president." Lewis later boycotted Trump's inauguration and first congressional address in protest.
Lewis said Wednesday he would need to decide "whether I can live with myself" if he goes to the new museum while Trump is in Mississippi, where Lewis was arrested jailed in 1961 for participating in the Freedom Rides. He said he'll visit the museum later if he skips this weekend's events.
The Mississippi Civil Rights Museum did not immediately respond to a request for comment.
Lewis' comments came hours after he joined 57 other Democrats to begin impeachment proceedings against Trump. He was the only Georgia Democrat to vote for the proposal.
"I think you have to send a signal," Lewis said. "You have to send a sign that it’s time for him to go.”
Read more: NAACP invites Trump to stay away from Mississippi museum opening