U.S. Rep. Edward Markey is challenging all Democratic and Republican candidates in the race to fill John Kerry's U.S. Senate seat to agree to keep outside groups from spending money on political ads.

The Malden Democratic said he wants a deal similar to the so-called "people's pledge" agreed to by former Republican Sen. Scott Brown and Democratic Sen. Elizabeth Warren in last year's Senate race.

That deal successfully discouraged outside political groups from spending money on television, radio and internet ads, although they did spend millions on campaign mailings.

Markey said the special election should focus on "big issues and ideas, not big-money outside groups."

Markey is the only announced candidate. U.S. Rep. Stephen Lynch is also weighing a run on the Democratic side.

Brown is also considering a run.