The U.S. Postal Service is warning states that it cannot guarantee all ballots cast by mail for the November election will be counted as the country ramps up preparations for larger numbers of mail-in votes amid the coronavirus pandemic.

The Washington Post reported Friday that the Postal Service sent warning letters to 46 states and the District of Columbia.

In letters sent to at least several states, including the key battleground states of Michigan and Pennsylvania, the Postal Service said there is "significant risk" voters will not have enough time to complete their ballots and return them on time under current state laws.

In its letter to Pennsylvania, the Postal Service recommended that completed ballots be mailed no later than October 27, a week before the November 3 election, to ensure they can make the Election Day deadline and be counted. Pennsylvania has said voters can request a ballot as late as October 27.

In response to the Postal Service's letter, Pennsylvania election officials late Thursday asked the state Supreme Court for permission to count ballots delivered three days after Election Day.

Many states have made it easier to vote by mail to address voters' concerns about public gatherings at election precincts during the coronavirus pandemic.

The Washington Post reports there are more than 60 lawsuits in the courts of a least two dozen states over the mechanics of mail-in votes.

Trump has repeatedly said, without evidence, that the November election could be rigged because of mail-in votes, claiming that Russia and China could forge U.S. paper ballots.

"This is going to be the greatest election disaster in history," Trump told reporters at the White House last month.

Trump has also said he does not want to wait "weeks, months or even years" for the results of the election because of problems he predicts will occur with mailed-in ballots.

Representatives for the National Association of Secretaries of State (NASS) and the National Association of State Election Directors (NASED) told VOA in July that if there is any evidence to support Trump's claims of potential mail-in ballot fraud, the administration has yet to share it with them.

On Thursday, Trump said he opposes emergency funding for the Postal Service to make voting by mail easier. However, on Friday he told reporters at a White House news briefing that he would agree to additional funding for the Postal Service if Democrats made concessions as part of a larger coronavirus stimulus bill. Talks on a new stimulus bill have largely broken down between Republicans and Democrats over sharp policy differences.

Most states already offer some form of mail-in voting, so-called "absentee" ballots, but because of the coronavirus pandemic, some states have moved to expand the use of mail-in ballots for the November election.