The Trump campaign and Republican National Committee have filed a lawsuit against Nevada's top elections official, alleging a recently passed bill that would automatically send all active registered voters a ballot for the November election would make "voter fraud and other ineligible voting inevitable."

"Many of [the bill's] provisions are head-scratching — particularly given the stark irregularities in Nevada’s June 2020 primary election, and because [the bill] changes so many election laws so close to the 2020 general election," the lawsuit, filed late Tuesday, reads. "Indeed, Defendant herself recently acknowledged that Nevada could (and should) successfully hold its 2020 general election without changing its election."

The lawsuit is seeking a court injunction to prevent Republican Secretary of State Barbara Cegavske -- who also opposed the bill but oversees the state's elections -- from implementing and enforcing the new law. The president's campaign and the RNC have pledged to spend about $20 million on election-related litigation fighting efforts to loosen voting restrictions during the coronavirus pandemic.

President Donald Trump had been threatening legal action. The state Senate passed the bill on Sunday in a party-line vote, and Democratic Gov. Steve Sisolak signed it into law Monday.

"Nevada has ZERO infrastructure for Mail-In Voting. It will be a corrupt disaster if not ended by the Courts. It will take months, or years, to figure out," Trump claimed on Twitter Wednesday morning.

And in a press briefing Tuesday, he claimed the United States Post Office wouldn't be able to handle the increase in mail: "In the case of Nevada, they are going to be voting in a matter of weeks. And, you can't do that, I can't -- imagine the Post Office could do it, all of a sudden they are supposed to be dealing with millions of ballots."

Trump reiterated that sentiment in his tweet Wednesday, differentiating Nevada from Florida, which he said "has built a great infrastructure, over years, with two great Republican Governors. Florida, send in your ballots!"

In an interview on CNN Tuesday night, Sisolak said expanding mail-in voting like this is "totally safe."

"My priority is to make sure the voters have every legitimate, legal option to vote. I think that this gives them that," he said.

Five states conduct all elections almost entirely by mail. Like Nevada, California, Vermont and the District of Columbia are planning to send ballots to registered voters ahead of the general election. There is no evidence of widespread fraud with mail-in or absentee voting.

In addition to mailing out ballots to voters in times of emergency, such as the current pandemic, the bill in Nevada also established requirements for the number of early voting and Election Day polling places in the state's two largest counties. Clark County, where Las Vegas is located, must have 35 polling places for early voting and 100 polling places on Election Day. Washoe County, where Reno is located, must have 15 precincts for early voting and 25 precincts on Election Day.

The Republicans' lawsuit also takes issue with this, alleging that it will lead to "disparate treatment with respect to rural voters" living in counties where only one vote center will be available, and therefore, is in violation of the Equal Protection Clause of the Fourteenth Amendment.

Nevada conducted its June 9 statewide primary almost entirely by mail. But most voters in Nevada typically vote in person, and those living in the state's largest counties -- where nearly 90% of the state's population resides -- faced longs lines on Election Day because only three polling places were open in Clark County and only one was open in Washoe County.

This report was featured in the Wednesday, Aug. 5, 2020, episode of “Start Here,” ABC News’ daily news podcast.