New York City’s sweeping mandate requiring nearly all private-sector businesses to ban unvaccinated employees from the workplace took effect Monday amid a spike in coronavirus infections. Proof of vaccination is also now required for children and teens to enter indoor public venues like restaurants and movie theaters, CBS New York reports.

Workers at roughly 184,000 businesses were required to show proof they have received at least one dose of a COVID-19 vaccine by Monday. Businesses that do not comply could face fines starting at $1,000, but Mayor Bill de Blasio has said imposing penalties will be a last resort.

“We’re implementing the strongest vaccine mandate in the country,” de Blasio said Monday on MSNBC’s “Morning Joe.” “This is what we need to do everywhere. Every mayor, every governor, every CEO in America should do vaccine mandates now. … 2022 has to be the year we leave COVID behind.”

Employers have to verify and keep a record of each worker’s proof of COVID-19 vaccination. Workers who have only gotten one shot will have to get a second one within 45 days. Companies must display a sign affirming they are complying with the rule “in a conspicuous location,” under the city’s mandate.

The new rules cover private places where work is performed in the presence of another worker or a member of the public. That includes not only stores, but shared work spaces and taxis, according to the requirements.

Businesses are not required to discipline or fire non-compliant workers, but they must keep them out of the workplace. Workers seeking an accommodation on religious grounds can come to work while their request is pending.

CBS New York notes that these are city rules and do not apply to businesses statewide.

Vaccinations are already required in the city for hospital and nursing home workers and for city employees, including teachers, police officers and firefighters. The city also enacted a vaccination requirement for dining indoors at a restaurant, going to a gym or seeing a show, which went into effect in August for adults.

Now enforcement of those rules is expanding to include children, too. Beginning Monday, anyone age 12 or older will be required to show proof that they are fully vaccinated to enter indoor public venues such as restaurants, museums, movie theaters and pro sports arenas. At least one dose is required for ages 5 and up.

“They are not major sources of transmission compared to adults, but yes, children do transmit to others. They transmit to other children, they transmit to people in the home,” Dr. Jennifer Lighter, a pediatric epidemiologist at NYU Langone, told CBS New York.

New York City has been slammed by a recent surge of cases from the highly contagious Omicron variant. On Sunday, transit officials announced that subway trains will run less frequently this week because so many staff members are out sick.

The city has also scaled back plans for this year’s New Year’s Eve celebration in Times Square.