Trump's campaign sued the Bucks County Board of Elections a week after the election, saying 2,177 absentee and mail-in ballots didn't adhere to code requirements.
The suit says those ballots did not have the voter's handwritten name, address or date on the return envelopes, and some were enclosed in "unsealed" privacy envelopes.
The appeal was rejected by the court, which is comprised of a 5-2 Democratic majority.
"Every illegal vote that is counted in an election undermines democracy and disenfranchises an American citizen who cast a legal vote," Trump's campaign said in its appeal, filed last Friday.
"And when such illegal votes are counted in some counties and not others, federal equal protection concerns are implicated."
In Bucks County, President-elect Joe Biden won by more than 17,000 votes, election results show. Biden won Pennsylvania by more than 80,000 votes.
Still, the Trump campaign is hoping to reverse that with at least five more appeals pending across Pennsylvania.
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