The NAACP and party officials for the Democrats, Republicans and Green Independents are scheduled to head to the state prison Wednesday for a voter registration drive.

Maine and Vermont are the only two states to allow prisoners to vote. The NAACP, working with the Maine Civil Liberties Union and the parties, want to make sure prisoners exercise that right, according to the MCLU.

“This has been an effective collaboration with the prison officials and with the party leaders, who are only working to register voters, not to promote a political agenda,” Rachel Talbot Ross, president of the Portland Chapter of the NAACP, said in a statement.

One of the NAACP’s three Maine branches is based at the prison in Warren.