President Donald Trump railed against governors who have considered turning their November elections toward a mail-in-only format, saying Tuesday the practice would invite massive fraud and could delegitimize the election.

Trump has previously threatened to withhold federal funding from states who choose to rely on mail-in ballots, but Democrats say the practice is necessary due to coronavirus. Republicans argue the integrity of the election is paramount and that polling places can operate safely under social distancing guidelines the same way grocery stores and other essential businesses have for months.

“There is NO WAY (ZERO!) that Mail-In Ballots will be anything less than substantially fraudulent. Mail boxes will be robbed, ballots will be forged & even illegally printed out & fraudulently signed. The Governor of California is sending Ballots to millions of people,” Trump tweeted. (RELATED: Mail-In Voting For November Election Over Coronavirus Opens Door For Fraud, Experts Say)

“Anyone living in the state, no matter who they are or how they got there, will get one. That will be followed up with professionals telling all of these people, many of whom have never even thought of voting before, how, and for whom, to vote. This will be a Rigged Election. No way” he added.

Republicans have joined Trump in pushing against calls for a mail-in election, launching the ProtectTheVote program in response. Nearly two-thirds of Americans believe mail-in ballots threaten the integrity of elections, according to a poll from the Republican National Committee.

“The RNC and the Trump campaign are aggressively fighting back against the Democrats’ assault on the integrity of our elections. All across the country, Democrats are trying to use coronavirus and the courts to legalize ballot harvesting, implement a nationwide mail-in ballot system, and eliminate nearly every safeguard in our elections,” the ProtectTheVote website reads.

California has already decided to send mail-in ballots to every registered voter before November, but other states are toying with the idea.

Under the U.S. Constitution, Trump has no authority to dictate how states conduct their elections, but he has instead found ways to influence their decisions by threatening funding cuts or, in other cases, the removal of planned political events.