Republican Sen. Scott Brown is refusing to participate in what his campaign is calling a "partisan Kennedy debate" after sponsors of the proposed match-up with Democratic challenger Elizabeth Warren labeled "inappropriate" Brown's demand that the widow of Democratic Sen. Edward Kennedy not endorse in the race.

Brown's campaign manager Jim Barnett said the response by the Edward M. Kennedy Institute for the United States Senate and the University of Massachusetts-Boston shows the institute can't hold a nonpartisan debate.

In a letter to Brown and Warren, representatives of the institute and school pointed out that newspapers and other media outlet routinely sponsor debates, and later endorse candidates.

Both organizations also sponsored a debate between Brown and Attorney General Martha Coakley in 2010.

Warren had previously agreed to the Sept. 27 debate.