Former New York Mayor Michael Bloomberg ramped up his efforts to fight gun violence Wednesday with a plan to spend $50 million on a grassroots network to organize voters on gun control.

The initiative's political target is the gun-rights lobby, including the National Rifle Association, which spends millions each year to back supportive candidates.

Bloomberg's group, called Everytown for Gun Safety, will focus on state and local lawmakers, corporate boards, and federal and state elections, including in Pennsylvania - "fields of play formerly occupied almost solely by the gun lobby," according to a statement.

In Philadelphia, a coalition of gun-control and antiviolence groups hosted an event at City Hall to launch Bloomberg's new organization here.

The billionaire Bloomberg told NBC's Today show he did not view his $50 million investment as a "heavy political lift."

"Thirty-one thousand Americans either get murdered or commit suicide with illegal guns," he said. "That's the heavy lift."

The staunch gun-control advocate bankrolled a $12 million ad campaign last year that promoted a failed effort for background checks and that targeted key senators.

The new initiative will focus on expanding background checks for gun buyers at state and national levels rather than on sweeping federal weapons bans that have been stymied in Washington.

The NRA, the largest U.S. lobby group for gun rights, spent $20 million in the 2012 election cycle, according to the Center for Responsive Politics.

The NRA, which claims nearly five million members, did not immediately respond to a request for comment.

Bloomberg will chair the new gun-control network, which includes the 1.5 million members of the existing groups Mayors Against Illegal Guns, which he cofounded, and Moms Demand Action for Gun Sense in America.

Mayor Nutter, who has been heavily involved in Mayors Against Illegal Guns and who was named a charter member of Everytown's board, spoke for more than 20 minutes at the City Hall kickoff, at times pounding on the lectern.

The issue of gun violence, particularly in the African American community, is a topic sure to rile the normally unflappable mayor. (He's been known to drop expletives on-camera to describe gunmen in the wake of shootings, but on Wednesday he stuck to the more printable "idiots.")

Nutter also sounded familiar themes of frustration with inaction in Congress and exasperation with the defender of the Second Amendment at all costs.

"This is literally a life-and-death circumstance," he said. "We've had enough death. I want more life."

Inquirer staff writer Troy Graham contributed to this article.