NPR: Changes at the U.S. Postal Service are forcing people who rely on postmarks when voting, filing taxes or mailing legal documents to be extra careful when cutting it close to deadlines.

Postmarks include the dates that USPS stamps on envelopes, and those are often used to determine whether a piece of first-class mail was sent on time.

But the Postal Service has proposed revising its mailing standards to say that postmark date “does not inherently or necessarily align” with the date that a mail piece was first accepted by a letter carrier or dropped off at a post office or collection box.

“In other words, the date on a machine-applied postmark may reflect the date on which the mailpiece was first accepted by the Postal Service, but that is not definitively the case,” USPS said in a recent Federal Register notice.

USPS hasn’t changed how it applies postmarks. What has changed is that, as the mail agency continues its controversial reorganization plan, more parts of the country may not get their first-class mail processed until the day after it’s collected by USPS.

That’s largely because the agency has reduced how often it picks up mail in certain areas more than 50 miles away from one of its new regional processing and distribution centers. The change, USPS says, “saves money, reduces carbon emissions, and benefits processing operations” at a time when fewer people and businesses are sending first-class mail compared to decades ago.

Still, in California, which is holding a special election for a closely watched ballot proposition on congressional redistricting, the USPS notice about postmarks has prompted state officials to urge eligible mail-in voters to drop off their ballots before Nov. 4.

“If you want your vote to count, which I assume you do because you’re putting it in the mail, don’t put it in the mail on Election Day” if you’re more than 50 miles from a USPS regional processing facility, California Attorney General Rob Bonta advised during a press conference this month, noting that a voter could consider turning in their ballot at an official vote center or drop box instead.

Read more: Why your mail may not be postmarked the same day it’s sent : NPR