President Donald Trump’s campaign filed a lawsuit Monday in Pennsylvania’s federal court in an attempt to block state election officials from certifying results showing President-elect Joe Biden carrying the swing state.

The lawsuit, brought by two registered voters and the Trump campaign, argues that Pennsylvania created “an illegal two-tiered voting system” by offering more oversight over in-person than mail-in voting. It claims the state’s mail-in voting system “lacked all of the hallmarks of transparency and verifiability that were present for in-person voters.”

In a separate complaint, a handful of Pennsylvania state legislators called for a legislative-led audit of the 2020 election and demand election results not be certified, nor electors be seated, until the audit is complete.”

Pennsylvania Gov. Tom Wolf‘s (D) office responded to the calls with a statement rejecting allegations of widespread voter fraud.

“Pennsylvania had a free, fair, and secure election,” the statement reads. “Millions of Pennsylvanians followed the rules allowed by the SCOTUS and each voter, regardless of political party, must have their voice heard. Allegations of fraud and illegal activity have been repeatedly debunked and dismissed by the courts. Those attacks against the core values of Americans are intended to undermine our democracy, and we must reject them.”

Wolfe added: “Pennsylvania is going to fight every single attempt to disenfranchise voters. We will protect this election and the democratic process. Pennsylvania will count every vote, and we will protect the count of every vote.”

Biden secured 49.8% of the vote, compared to Trump’s 49.1%. The key swing state, which voted for Trump in 2016, was conducted largely by mail due to the coronavirus pandemic. Over 2.6 million voters in Pennsylvania voted by mail, per the U.S. Elections Project. The vast majority of mail-in votes were cast by Democrats (1.69 million compared to about 620,000 Republicans).

It was widely expected that the state’s initial results would skew Republican, as more GOP voters cast their ballots in-person. And in Pennsylvania, election officials could not even begin processing mail-in ballots until polls closed, which is why it later flipped blue.

The Pennsylvania case is just one of many lawsuits brought forth by Trump attorneys as an attempt to undermine the election results and contest his loss in a court of law. Other cases have already been thrown out in Georgia and Michigan.