(Reuters) - The largest law firm representing the Trump campaign or its allies in post-election litigation challenging votes in key states has withdrawn from an election lawsuit in Maricopa County, Arizona.

Associate Presiding Civil Judge Daniel Kiley on Tuesday granted Snell & Wilmer's request to withdraw as counsel of record for the Republican National Committee. The RNC had teamed-up with the Trump campaign and the Arizona Republican Party in the case, which alleges that Maricopa County incorrectly rejected some votes cast on Election Day.

Snell & Wilmer partners Brett Johnson and Eric Spencer first moved to withdraw on Sunday, a day after the case was filed. Johnson and Spencer did not respond to requests for comment. Snell & Wilmer chairman Matthew Feeney said the firm doesn't comment on its client work.

Two other large law firms that have represented the Trump campaign in election litigation, Jones Day and Porter Wright Morris & Arthur, have faced an onslaught of online criticism this week from critics who say the cases erode confidence in the democratic process, sparked by a Monday New York Times story focused on the firms' roles.

President Donald Trump has refused to concede the election since major news outlets called it for Democrat Joe Biden on Saturday.

Porter Wright has filed lawsuits since Saturday contesting mail-in ballots in Pennsylvania.

Jones Day, which is not representing the campaign or others in post-election litigation, filed a Pennsylvania mail-in ballot lawsuit in June and serves as outside counsel to the Trump campaign. It defended its work in a statement Tuesday.

Porter Wright also defended its political law work in a Wednesday statement, noting it has represented Democratic campaigns and issues as well as Republican ones.

Snell & Wilmer's withdrawal from the Arizona case leaves Porter Wright as the largest law firm pressing the Trump campaign's post-election litigation claims. Porter Wright has about 210 lawyers listed on its website. Jones Day has about 2,500 lawyers.

Snell & Wilmer, a Phoenix-based firm with about 440 lawyers spread across the western United States and Washington, D.C., was working on the Arizona case alongside Phoenix political law firm Statecraft. That firm, which declined to comment, is still representing the Republican challengers.

An evidentiary hearing is set for Thursday in the lawsuit, which the Arizona Secretary of State described as a case of "grasping at straws" in a statement to Reuters.

The plaintiffs are seeking an order requiring a manual review of purportedly overvoted ballots that were cast in-person. They're also asking a judge to bar the certification of the vote until the review is complete.

Snell & Wilmer, which has an election law practice, is separately serving as co-counsel in the Arizona Republican Party's long-running defense of a state law that prohibits absentee ballot collection by third parties and the counting of ballots cast at the wrong polling precinct.

That case, first filed in 2016, is pending before the U.S. Supreme Court. Snell & Wilmer's co-counsel in the case is Jones Day.

Snell & Wilmer received more than $770,000 from the RNC, the National Republican Congressional Committee and the National Republican Senatorial Committee for legal services and legal consulting between January 2019 and September 2020, according to Federal Elections Commission records.

A Trump campaign spokeswoman did not immediately respond to requests for comment.