Political activist Leonard A. Roberto today will announce his plan to challenge State Sen. Dale M. Volker of Depew in the September Republican primary.

Roberto, 54, ran against Volker in the 2006 GOP contest and came close to winning Erie County before the incumbent drew on his strength in Wyoming, Livingston and Ontario counties to win the race.

His latest effort complicates another potential challenge to Volker by Erie County Republican Chairman James P. Domagalski, who said in January he is thinking about entering the race. Other party sources also have observed that if Domagalski does not challenge Volker, some other Republican will.

“My goal is to oppose any real dollar spending increases in the state budget, and I propose that total dollar spending be reduced by 20 percent over the next two years,” Roberto said in a statement. “I will propose to work on reforming Medicaid and will propose legislation to review and reform Medicaid . . . including proposing legislation which prohibits the state from passing Medicaid costs on to county government.”

In 2006, Roberto founded an organization called Primary Challenge, which encourages party members to run against entrenched elected officials in primary elections.