The U.S. Postal Service is reminding voters that to ensure their mail-in votes are counted, they need to place their ballots in the mail by Tuesday; otherwise, their ballots might not arrive in time.Nearly three-quarters of the U.S. states require ballots to be received on or before Election Day, including six of the top seven battleground states in the presidential election. Nevada is among a handful of states that will accept ballots after Election Day if they are postmarked by Election Day.USPS said that 99.9% of ballots mailed by election officials during the 2020 election were received by voters within a week. On average, outbound ballots took two days to reach voters.RELATED STORY | Republicans ask US Supreme Court to block counting of some provisional ballots in PennsylvaniaFor voters returning ballots, USPS said 98.3% of ballots were received by election officials within three days, and on average, it took just a day for ballots to reach election officials.USPS said it implements "extraordinary measures" to ensure ballots are sent and received on time. USPS said it uses extra deliveries and collections, special pick-ups, specialized sort plans at processing facilities to expedite delivery to boards of elections, and local handling and transportation of ballots.The postal service said it expects its performance to match its ability to shuffle mail-in ballots in time for Election Day.To see when ballots are due in your state, visit vote.org.RELATED STORY | Debunked fake video purports to show destruction of ballots in PennsylvaniaThe practice of mail-in voting has faced more scrutiny from Republicans and supporters of former President Donald Trump since the 2020 election. While Trump generally performed well among votes cast on Election Day, he struggled in key battleground states with mail-in ballots.He has since criticized mail-in voting as not being secure.The National Conference of State Legislatures says mail-in voting helps boost turnout and gives voters the ability to study their ballot without time constraints.But the NCSL notes that mail-in ballots are subject to a higher rate of errors, that they take longer to count, and the potential for coercion from family or other members of a household.