A coalition of political activist and self-styled reform groups announced this afternoon that three of five Democratic candidates for mayor have signed a pledge to support public financing in future Philadelphia campaigns.

So did the lone Republican candidate, Al Taubenberger.

Democrats Chaka Fattah, Dwight Evans and Michael Nutter signed on, while Bob Brady and Tom Knox did not, the coalition said at a press conference outside City Hall. Nutter was the only mayoral candidate to show up at the event.

Knox has spent more than $6 million of his own money on the race thus far, prompting complaints of an unlevel playing field from Brady's supporters, among others.

The coalition making today's announcement included MoveOn.Org, Common Cause/Pennsylvania, Philadelphia Forward and Public Campaign Action Fund. Young PhillyPolitics.com, a blog, also joined the effort in soliciting candidates to take the coalition's so-called "Fair and Clean Elections Pledge."

Changing the city's election system to one that relies on public financing would require action from Harrisburg. Evans, who is chairman of the state House Appropriations Committee, has been leading a push for such a change since last year.

The coalition said 29 City Council candidates, including eight incumbents, have also signed its pledge, which reads:

"I pledge that, if elected, I will support a comprehensive fair and clean elections system for Philadelphia, like those found in several states and cities, that will level the playing field, reduce spending on elections, and end the conflicts of interest caused by campaign contributions. I will work to enact full public funding for qualified municipal candidates who agree to take no or little private money, making Philadelphia a national leader in ethics and campaign finance reform."

Contact staff writer Marcia Gelbart at 215-854-2338 or mgelbart@phillynews.com.