Armed with a new state law, pro-gun groups are rapidly scaling up their attack on municipal firearms ordinances in Pennsylvania, with the National Rifle Association filing suit over gun-control measures in three cities.

The cities of Philadelphia, Pittsburgh and Lancaster have "openly defied" a 40-year-old state law that forbids municipalities from regulating firearms, said Chris Cox, executive director of the NRA's Institute for Legislative Action.

The lawsuit against Lancaster was filed late Tuesday and was released by the NRA on Wednesday. The group also filed legal paperwork in Philadelphia and Pittsburgh courts and was awaiting confirmation those lawsuits had been accepted.

Another group, Houston-based U.S. Law Shield, sued the capital city of Harrisburg on Tuesday over its gun laws.

Pennsylvania has long barred its municipalities from approving ordinances that regulate the ownership, possession, transfer or transportation of guns or ammunition. But scores of cities and towns ignored the prohibition, and gun-rights groups complained the local measures were difficult to challenge successfully in court because judges have ruled that plaintiffs could not prove they were harmed by them.

Under a state law that took effect last week, gun owners no longer have to show they have been hurt by a local ordinance to successfully challenge it. The new law also allows organizations like the National Rifle Association to sue on behalf of any Pennsylvania member. If successful, the challenger can also seek legal fees and other costs.

Philadelphia, Pittsburgh and Lancaster are fighting the new law in court, contending lawmakers didn't follow constitutional procedure for passing legislation.

Philadelphia officials have long said the local measures are needed to combat persistent gun violence that claims hundreds of lives each year. In 2010, the Pennsylvania Supreme Court tossed city ordinances that limited people to buying one gun a month and banned assault weapons, but the NRA -- deemed to lack standing -- lost its bid to get three other city gun laws thrown out.

In the small city of Lancaster, the NRA is challenging an ordinance that requires residents to tell police if a gun they own is lost or stolen. Such ordinances are common in cities throughout Pennsylvania.

Lancaster Mayor Rick Gray, who is named as a defendant along with City Council and the city itself, did not immediately respond to an email request for comment made through his chief of staff.

Cox, the NRA official, said local laws "do not make people safer" and, in a statement, accused officials of "politically grandstanding at taxpayers' expense."

The NRA plans to go after other municipalities whose gun ordinances are barred by state law, said the group's attorney, Jonathan Goldstein.

"We expect every municipality to repeal ordinances that are pre-empted. If other folks don't get on board with what the law requires, they can expect to hear from us in due course," he said.

Under threat of litigation by another attorney, Joshua Prince, more than 20 Pennsylvania municipalities have already moved to repeal their firearms ordinances instead of defending them in court.