In Pennsylvania's heated senatorial race, gun control is taking center stage.

CeaseFire Pennsylvania, an advocacy group working against gun violence, has endorsed Katie McGinty, Democratic candidate for U.S. Senate, who's looking to unseat Republican incumbent Sen. Pat Toomey.

"I am honored to have the support of CeaseFire Pennsylvania in this race," McGinty said in a conference call Wednesday. "This organization's advocacy and leadership have been critical in the urgent effort to pass common ground and common sense gun safety initiatives."

McGinty's backing comes on the heels of two high-profile gun-control endorsements for her opponent.

Erica Smegielski, the daughter of a principal slain during the Sandy Hook Elementary massacre, and Gabrielle Giffords, a former U.S. representative who was shot in an attempted assassination in 2011, backed Toomey earlier this month, praising his actions in support of gun control after Sandy Hook.

In 2013, Toomey crossed party lines to vote in favor of a bill that would help prevent felons, domestic abusers and the dangerously mentally ill from purchasing firearms at gun shows and from online retailers. That bill failed, but Toomey still supports it, and voted for it when it was reintroduced in 2015.

After CeaseFire Pennsylvania announced its support of McGinty, Toomey's office criticized the group for being "hyper-partisan."

"The gun safety organizations that are serious about achieving bipartisan results, such as those of Gabby Giffords and Michael Bloomberg, are supporting Pat Toomey," Ted Kwong, communications director for Toomey's reelection campaign said in an email. "It’s a shame that [CeaseFire Pennsylvania] has become so hyper-partisan that it undermines the very goals it claims to believe in, because nothing will happen in Congress on this important issue without bipartisan support."

Meanwhile, McGinty's campaign has accused Toomey of backpedaling.

"Toomey has let others assume the mantle of leadership. Aside from an unsuccessful attempt to revive the bill in December 2015 following the San Bernardino shooting, Sen. Toomey has chosen to focus on other issues," McGinty's campaign said in a press release Tuesday, citing Toomey's support of the Constitutional Concealed Carry Reciprocity Act, which would force Pennsylvania to accept gun permits from more lenient states.

While Toomey and McGinty have both supported broad background checks for prospective firearm owners, the two differ in other areas of gun control:

On assault weapons, Toomey has rejected bans of "entire classes of commonly owned firearms," he wrote in an op-ed the   Philadelphia Inquirer

"Such bans do not target criminals or terrorists. They sweep in millions of law-abiding Americans and prevent them from exercising their constitutional rights," the senator wrote.

Toomey is also against bans on large ammunition clips.

McGinty hit her opponent over both issues in an ad released earlier this month. She supports bans on assault-weapon ownership and high-capacity magazines.

Pennsylvania voters generally support background checks on all gun purchases, an issue that has crossed party lines. According to Public Policy Polling, 87 percent of voters support the checks. PPP also polled 58 percent of voters supporting a nationwide ban on the sale of assault weapons.

In the same survey, conducted from July 29 to July 31 of about 1,500 likely voters, 42 percent disapproved of Toomey's job performance, with 32 percent approving and 27 percent saying they're not sure. McGinty had similarly split results: 25 percent favorable opinion, 37 percent unfavorable, 38 percent unsure.