Metro Transit driver Jean Mier has a gentle but forthright message for passengers who eschew a mask when boarding her bus.

"Where's your mask?" she asks, pointing to her own.

As COVID-19 spreads rapidly through Minnesota, Metro Transit began deploying its police force Wednesday to encourage passengers to wear masks as a way of stemming the pandemic's deadly reach.

Most of the riders on Metro Transit's Route 5 bus in Minneapolis and Brooklyn Center earlier this week were appropriately masked. Some passengers said they didn't have a mask, prompting Mier to give them a few from her stash. One maskless customer glared at her, pushed his way onto the bus and neglected to pay his fare, too.

Mier sighed and shook her head slightly. Her job is to safely drive the bus and stay on schedule, not badger people about wearing masks.

Under the new rules, Metro Transit police officers will engage in "additional education and encouragement," reinforcing the importance of wearing masks on public transportation and handing out masks to those who need them, said Brian Funk, Metro Transit's deputy chief operating officer for bus operations.

If passengers refuses to don a mask, they may be asked to leave the bus or train, Funk said. Chronic offenders may be issued a citation and fined up to $100, according to Gov. Tim Walz' executive order.

Officers will focus much of their efforts on bus routes 10, 17, 21, 54 and 74 and Green Line light rail, which have a higher level of passengers forgoing masks, according to a bulletin issued Wednesday to Metro Transit operators.

"When it comes to enforcing public health guidelines, there's a real struggle with these types of conversations about enforcement," said Kumi Smith, an assistant professor in the Division of Epidemiology and Community Health at the University of Minnesota.

Communication, she said, is critical: "The point is not to explain there are rules, but to point out the motivation for following the rules and why it's important."

In recent months, Metro Transit has compiled data about mask compliance through on-the-street and remote camera observation. On some buses, 70% to 87% of the passengers wore masks.

"Of course, on some buses it wasn't nearly that high," Funk said. "We believe we're very safe, but everyone needs to do their part."

Metro Transit's stepped-up efforts come after the federal Centers for Disease Control and Prevention (CDC) issued new guidance last month urging masks for all passengers on public transportation and operators of buses and trains.

Traveling on public transportation "increases a person's risk of getting and spreading COVID-19 by bringing persons in close contact with others, often for prolonged periods, and exposing them to frequently touched surfaces," the CDC said.

The agency also noted that social distancing is often difficult on public transportation.

Metro Transit has tried to promote social distancing by limiting the number of passengers on buses to 10 to 15 people, depending on the vehicle's size. That goal is a bit easier to achieve because overall ridership on local buses is down about 62% since last spring.

The transit agency says it has stepped up cleaning of buses and distributed alcohol wipes to drivers to scrub fare boxes and other high-touch areas. It's also experimenting with a new air filtration system on some buses that emits pulses of hydrogen peroxide to kill the airborne virus. Plexiglass shields have been installed on buses to separate drivers from passengers.

To date, no Metro Transit bus drivers or light-rail operators have died of COVID-19, though 99 have contracted the virus since last spring.

Some drivers say a fair share of passengers thwart the mask mandate, often by pulling masks down around their chins once they sit down or by leaving their noses exposed. Those outliers concern many drivers.

On Mier's route earlier this week, a woman removed her mask as she attempted to unfurl a dollar bill for the fare box.

Failing that, she tried to smooth the money with her mouth. Once she sat down, she proceeded to eat her lunch, asking nearby passengers if they wanted to share.

"I don't want to get infected, but I don't want people who ride on my bus to get infected either," said Kenneth Dolney Jr., who has been a Metro Transit bus driver for 32 years. He added that some passengers lash out when he encourages them to wear a mask.

The safety of drivers, light-rail operators and other employees during the pandemic has emerged as a central issue in contract negotiations between the Amalgamated Transit Union and Metro Transit, said Ryan Timlin, president of Local 1005. The union has voted to strike if negotiations stall, though talks are scheduled Friday.

"Employees have a high risk of catching the virus because of work conditions," Timlin said. "Pretty much on every trip one person or more is not wearing a mask."

Twitter: @ByJanetMoore