PHILADELPHIA — Elections officials in multiple Pennsylvania counties are warning that an impending change to voter registration deadlines — a measure meant to increase political participation — would add significantly to their preelection workloads, potentially causing confusion for voters at the polls and unintentionally disenfranchising people in 2020.

The change is part of a wide-ranging elections bill negotiated behind closed doors by Gov. Tom Wolf, a Democrat, and Republican leaders who control the state Legislature. The bill represents the most significant changes to Pennsylvania’s electoral system in decades, including allowing all voters to cast absentee ballots by mail and extending deadlines to return them.

The Legislature gave final approval Tuesday to the bill, which Wolf said he would sign.

“This bipartisan bill creates the most significant improvements to our elections in more than 80 years. Pennsylvania has gone from collectively being the state least friendly to voters to a national leader in voting and election security reforms,” he said in a statement.

But the proposed change to the voter-registration deadline surprised and alarmed the county officials who run elections. Closing the registration window 15 days before an election, instead of the current 30 days, would require more staff to process registrations and increase the number of voters who are not in poll books. That, officials warn, could unintentionally disenfranchise voters by increasing their chances of running into problems at the polls, including waiting in long lines or needing provisional ballots. In the worst-case scenario, some registrations might not get processed in time.

“It could really risk having a detrimental effect on the election,” said Lisa Deeley, chair of the Philadelphia Board of City Commissioners. She estimates the change could cost Philadelphia about $2 million.

“We could inadvertently be causing more grief for voters than this is helping in the end,” said Jeff Greenburg, Mercer County elections director.

“It’s creating an unnecessary situation where we really don’t need one,” said Gerald Feaser, head of elections in Dauphin County.

A spokesperson for the governor said the administration will work with counties to ensure having the resources necessary to enact the changes and noted that extending the voter-registration deadline “has been long sought by election advocates.” (Pennsylvania’s current 30-day deadline is one of the earliest in the country, and many states have already moved to same-day registration, allowing people to register on Election Day and cast a ballot.)

County officials said their concern is administrative, not ideological, and in many cases said they support the change, just not its implementation. The concerns come from both Republican and Democratic counties.

There’s an election next week. It will take time to certify those results, and then the presidential primary is in April, five months later. That’s not enough time, Deeley said, to make such a big change to how her office does its work.

“I am for all these changes,” said Deeley, an elected Democrat. “I think they’re a long time coming. But even the best ideas, if implemented poorly, turn into bad ideas. And five months really is not a responsible amount of time for us to be able to cut a process in half.”