The top election official in Philadelphia is warning that a minor technicality in a new state Supreme Court ruling could cause as many as 100,000 mailed ballots to be rejected statewide in the November election, a potentially significant statistic for a state that President Trump won by about 44,000 votes in 2016.

Lisa Deeley, the Democratic chairwoman of Philadelphia’s election board, warned in a letter to lawmakers this week that the court’s requirement of an additional envelope for voters to mail back with their ballots could disenfranchise tens of thousands of voters in her city and many more statewide.

At issue is the use of “secrecy envelopes,” which are designed to protect the privacy of the voter. A voter returning an absentee ballot must insert the ballot into the secrecy envelope, and then insert that envelope into a larger envelope that carries the mailing address and postage.

For the state’s primary election, local election officials were allowed to accept ballots that were returned without the inner envelope — commonly referred to as “naked ballots” — to accommodate the surge of voters in Pennsylvania who cast absentee ballots for the first time because of the coronavirus pandemic.

But under last week’s court ruling, ballots sent back to election officials without the inner envelope will be rejected, with no opportunity for voters to rectify the problem to make sure their vote is counted.

“It’s just so unfair that we’re disenfranchising people that have done everything right,” Deeley said. “They applied for the mail-in ballot, they got the mail-in ballot, they voted by the mail-in ballot, they put it in an envelope, returned to us on time — and all because of a technicality, their vote isn’t going to count.”

Pennsylvania is one of roughly 16 states that require such an inner envelope, according to a tally by the National Conference of State Legislatures. But some states decided to waive that requirement for the general election, which they said would save time for election officials who anticipate processing a record number of mail-in ballots this fall.

For example, Georgia eliminated the inner envelope for the primary. According to Georgia state law, election officials can still count absentee ballots even if they are not returned in an inner envelope, providing more flexibility to voters and election officials.

Other states will continue using the inner envelope and are holding voter education campaigns to remind voters to read and follow the instructions for mailing them in.

In New Jersey, for example, state officials are sharing pithy instructions: “Vote, sign, seal, return.” The “sign and seal” refers to steps that voters need to take for the inner envelope, before they place it in a larger envelope to return it, serving as a reminder for voters to include the inner envelope when they return their ballots, said Alicia D’Alessandro, spokeswoman for the New Jersey secretary of state.

“We’re focused on making sure the voters know how to properly cast their ballot if they’re going to be using a vote-by-mail ballot,” D’Alessandro said.

The idea behind secrecy envelopes is to ensure that an election official opening the mail to process a voter’s ballot is not able to match voters’ name with how they voted, thereby ensuring privacy for the voter, said Michael Thorning, associate director of governance at the Bipartisan Policy Center.

But much of that processing work is now done by machines that process high volumes of envelopes at a time, and in many states, an elections official only gets involved after the ballots have been separated from any identifiable information of voters, Thorning said.

“We don’t have any evidence, any reporting — I’ve never even heard of anecdotal evidence — of problems where election workers were trying to match these [ballots] up,” Thorning said.

With the heightened interest in mail-in voting for the November elections, Thorning said voters need to be aware of such logistical and technical challenges they may face in returning their ballots, and that they need to read and follow instructions carefully.

“As many states are for the first time using widespread voting by mail, that’s forcing issues to the surface that probably were very rare in prior elections, and potentially could become big ones now,” he said.

In Pennsylvania, voters will be able to vote in a presidential election for the first time by mail without providing an excuse for requesting mail-in ballots. With more Pennsylvanians voting by mail than in previous years, Deeley said she is worried that many of the first-time mail voters’ ballots will be rejected because of the envelope glitch.

The envelopes are a vestige of the past, when ballots were counted at the precinct levels and therefore election officials wanted to ensure privacy for voters, Deeley said. Now, ballots are counted at a central location using a machine that separates thousands of envelopes from ballots per hour, and the requirement is no longer necessary, she said.

With absentee voting already underway in Pennsylvania, Deeley is urging state lawmakers to eliminate the envelope requirement.

The exact statewide number of ballots that were returned without the inner envelope in the 2020 primaries is unknown because those ballots were deemed eligible and counted, state officials said.

But in the 2019 general election, 6.4 percent of the 3,086 absentee ballots cast in Philadelphia alone were rejected because of missing inner envelopes. That same percentage would have resulted in about 11,211 naked ballots in the 2020 primary, Deeley said, adding that the number is likely to be a low estimate because of the increase in the number of people voting absentee for the first time in that election.

Voting-rights advocates said they are concerned with requirements that create more opportunities for voters to make mistakes and potentially make it less likely for their ballot to count.

But they said they are hopeful that the new state Supreme Court ruling has drawn new focus on the envelope requirement and that voters pay attention before they return their ballots to the election officials.

“The silver lining of this decision from the state Supreme Court is now that we know the rules, we can educate voters about the rules,” said Suzanne Almeida, director of Common Cause Pennsylvania, a good-government group that works on voter access matters.

“And I have every confidence that voters can learn the rules right. There are plenty of ways, plenty of places in election law where we require voters to know specific steps that they need to take. This is just one more of those,” Almeida said.

Elise Viebeck contributed to this report.