Congressional candidate Carol Shea-Porter is attacking her opponent, U.S. Rep. Frank Guinta (R-N.H.), over his refusal to co-sign a statement asking large political action committees to stay out of their race.

Shea-Porter, a former congresswoman from Rochester, lashed out at Guinta after his campaign sent out a fundraising letter at the end of June. The letter said several liberal organizations, including a Super PAC from San Francisco, are spending millions of dollars on Shea-Porter’s behalf in New Hampshire.

In response, Shea-Porter urged Guinta to co-sign a statement asking Super PACs to stay out of the race. According to her campaign, Guinta refused.

“If he is sincere about his fears, he can call my office and we will sign a statement together this very weekend, asking Super PACs to stay out of our race,” Shea-Porter said in a statement released on July 6.