The Cook County Clerk Monica Gordon said the change could delay or even invalidate vote-by-mail ballots, if not postmarked in time.
Previously, mail was postmarked the day you dropped it in the mailbox, now, it will be postmarked the day it's processed at the post office, which can sometimes be days later.
The new USPS postmark policy comes just weeks ahead of the Illinois Primary Election on March 17.
Some suburban Cook County courthouses, 69 W. Washington Pedway and Melrose Park Village Hall begin early voting February 18.
The rest of the traditional county voting sites open on March 2.
2026 elections: What to know about major political races in Illinois this year
The clerk says she believes this may possibly wreak of voter suppression, and that's why she pleading with voters to ensure their ballots are counted.
"We've been told that this is just due to procedural changes. I don't know the motive of the change, but what I do know that it is ill timing. We got to do what we can to make sure that we get those ballots in," Gordon said.
Gordon recommends sending your mail-in ballot the week before Election Day just to be safe.
Other secure voting options include early in-person voting and ballot drop boxes, if you want to avoid lines on Election Day.
2026 primary elections: Click here for voter information in Illinois, Indiana, Wisconsin
SEE ALSO: ABC7 Chicago presents 2026 Democratic U.S. Senate Primary Forum