The candidates believe Mayor Ed lee's campaign has engaged in improper activities targeting Cantonese-speaking voters.
One complaint specifically mentions special plastic stencils being handed out that prevent voters from selecting a candidate other than lee.
Lee's campaign denies any involvement.
The seven candidates behind the letter include public defender Jeff Adachi, city attorney Dennis Herrera, former supervisor Michela Alioto-Pier, businesswoman Joanna Rees, state senator Leland Yee and current supervisors David Chiu and John Avalos.
