Voting in Pennsylvania’s May 17 primary election is underway, with 164,000 voters already casting their ballots by mail, according to the latest Department of State data. On the line are party nominations for U.S. Senate, governor, U.S. House, and state legislative seats.

» READ MORE: Pa. Voter Guide: May 17, 2022

Registered voters in Pennsylvania have until Tuesday to join the more than 831,000 residents who have already requested mail ballots, slightly outpacing the requests made for last year’s municipal primary.

Pennsylvania has tight mail ballot deadlines — ballots can be requested up to one week before election day but must be received by county elections officials by 8 p.m. on election day. That means postmarks don’t count, and mail ballot drop boxes are locked at 8 p.m.

Because it can take time for ballot applications to be processed, printed, and delivered — and a few days for the ballots, if mailed back, to be returned — elections officials encourage voters to return ballots as soon as possible.

In the days right before election day, when there might not be enough time for the ballot to be returned by mail, voters can hand-deliver their ballot to their county elections office or, if set up, a drop box.

Philadelphia has 16 mail ballot drop boxes this election, and voters can also visit the elections office in Room 140 of City Hall to vote early by requesting, filling out, and returning a mail ballot in one visit. Other counties have also set up drop boxes for returning ballots.

“They definitely don’t want to drop that ballot into the mailbox too close to May 17, because we want to assure that their vote is counted,” Leigh Chapman, acting secretary of state, told reporters Thursday.

And while election mail is expedited, Chapman reminded voters that deliveries are currently taking about three days.

The mail voting is being driven primarily by Democrats, as a strong partisan divide continues in vote method.

Republicans, driven by Donald Trump’s lies about vote fraud and the 2020 election being stolen, largely avoid mail voting. Democrats are much more likely to vote by mail than Republicans are, though they may also be returning to in-person voting on election day as the primary method of casting votes. (In the 2020 election, for example, most of Joe Biden’s votes were cast by mail; last year, most Democratic votes were cast in person.)

More than 8.7 million Pennsylvanians are registered to vote, consistent with last year’s registration numbers of 4 million Democrats and 3.4 million Republicans.

For those voting in person May 17, polls open at 7 a.m. and close at 8 p.m. COVID-19 precautions will be left to individual counties.