David McCormick has filed a lawsuit challenging at least 15,000 provisional ballots in Philadelphia, Pennsylvania Senate race, hours after claiming victory over the Democratic senator Bob Casey.

McCormick, a Republicanhad a slight lead over Casey in Friday’s Senate election in the battleground state. McCormick’s campaign declared victory, but Casey didn’t concede the race, just like that Democrats note that there are still some ballots outstanding and the race may reach the threshold for an automatic recount. The Associated Press projected McCormick as the winner with 97 percent of the vote counted, but other outlets did not call the race.

On Friday, McCormick’s campaign filed a legal challenge to 15,000 to 20,000 provisional ballots in Philadelphia, a Democratic stronghold.

The petition, reported by The Philadelphia Inquirer, calls for the campaign to be able to challenge these provisional ballots in groups, rather than contesting individual ballots – as well as to “seize provisional ballots cast by voters” who originally cast their mail-in ballots but had those rejected ballots.

Provisional ballots are given to voters who believe they are registered to vote but whose names do not appear on the polling station registration list. Election officials then work to determine if the person was registered to vote.

McCormick’s lawyers wrote that these ballots could have a “potential impact on the outcome of the election,” despite previously claiming victory.

“A preliminary injunction is necessary to prevent the immediate and irreparable harm that could result from counting these provisional ballots without proper judicial review. The potential inclusion of improperly counted ballots would compromise the integrity of the election process and violate the rights of plaintiffs.” the file says.

In a statement to Newsweek, Elizabeth Gregory, a spokeswoman for McCormick, said: “Yesterday, due to his insurmountable lead in the vote count, the AP called the race for Dave McCormick, officially naming him the next senator for Pennsylvania. Dave is honored to have earned the support of all Pennsylvanians. across the Commonwealth and looks forward to serving them in the United States Senate.”

Maddy McDaniel, a spokeswoman for Casey, criticized the lawsuit in a statement to Newsweek.

“The number of provisional ballots expected in areas that favor Senator Casey, such as Philadelphia and its suburbs, is further evidence that this race is too close to call,” the statement said. “As the McCormick campaign acknowledged in its own lawsuit this morning, the counting of these ballots could have an ‘impact on the outcome of the election.’ With more than 100,000 ballots still to be counted, we will continue to make sure the voices of Pennsylvanians are heard.”

McCormick led by less than 35,000 votes, and Democrats are hoping any provisional ballots in Philadelphia and its suburbs could tip Casey, or at least keep the race close enough for a recount.

However, there are still several notable voters in Republican-leaning Cambria County, fueling GOP optimism that McCormick’s lead will hold.

The Pennsylvania government website reported the totals as 3,340,611 for McCormick and 3,308,681 for Casey as of 4:45 p.m. ET Thursday, a difference of about 0.47 percent.

If the race remains less than or equal to 0.5 percent of the total vote, it would trigger an automatic recount, according to state law. Candidates can also request a recount with no margin required and no deadline set for completion.