MADISON, Wis. (AP) — Voting advocacy groups and the mayor of Wisconsin's largest city on Tuesday urged Gov. Tony Evers to close polling sites and conduct the state's spring election entirely by mail to protect voters and a dwindling pool of election workers from the coronavirus.

Evers has refused calls to postpone the April 7 election in the face of the crisis. The election features the state's presidential primary, a state Supreme Court race and hundreds of races for local office. Most local officials terms expire April 21 and delaying the election could leave those spots vacant, Evers has argued. However, the governor said Monday he was considering conducting the election entirely by mail.

A coalition of voting advocacy groups that includes the League of Women Voters' and the American Civil Liberties Union's Wisconsin chapters issued a statement Tuesday calling on Evers to send absentee ballots to every registered voter in the state.

“Absentee voting offers advantages over a traditional polling place, especially now," LWV Wisconsin Executive Director Debra Cronmiller said. "It will keep all of us safer, and help people across the state make their voices heard in this important election.”

Milwaukee Mayor Tom Barrett sent Evers and Republican legislative leaders Robin Vos and Scott Fitzgerald a letter on Monday warning that in-person voting is no longer feasible or safe.

Barrett noted that the Milwaukee Elections Commission on Sunday was forced to close its three early in-person voting sites because the sites were losing staff daily. He added that more election workers, including chief inspectors, have quit in anticipation of Evers' issuing an advisory to stop all nonessential travel.

“This is very real,” Barrett wrote. “In good conscience I would not ask one of my loved ones to sit in a room for hours greeting dozens of people during this pandemic. I can't expect citizens of my city to do that either.”

He said every day spent preparing for in-person voting is a lost opportunity for municipalities to retool their systems to meet heavy demand for absentee ballots.

Wisconsin law grants the governor a host of special powers in a public health emergency, including the authority to issue any order he or she deems necessary to protect people and property and suspend any administrative rule if compliance prevents, hinders or delays a necessary response action. It's unclear if Evers could cite those provisions as authority for making changes to the election, however, since little case law exists on how to conduct elections during such emergencies.

Wisconsin Elections Commission spokesman Reid Magney had no immediate comment.

Local election clerks had received 554,116 absentee ballot applications as of Tuesday morning, according to the commission. Clerks issued 249,503 ballots in the state's 2016 spring presidential primary.

Voters can request absentee ballots through April 2.

U.S. District Judge William Conley on Friday ordered the commission to extend online voter registration through March 30. Voters must be registered before they can cast an absentee ballot. Online registration was supposed to end March 18 but Democrats argued the deadline should be extended to give people more time in light of social distancing disruptions.

Democrats also argued that clerks should be given more time to receive absentee ballots given the crush of applications. Right now ballots must be in clerks' offices by 8 p.m. on election night to count. Conley didn't rule on that question Friday.