New York City public schools have opened to about a million school students in the nation’s largest experiment of in-person learning during the pandemic as the city was embroiled in an arbitration United Federation of Teachers, which represents almost 80,000 teachers in city public schools, over issues including accommodations for teachers who say they have health issues that prevent them from being vaccinated.

The start of the school year coincides with several milestones in the city’s pandemic recovery that hinge on vaccine mandates.

Nearly all of the city’s 300,000 employees will be required to be back in their workplaces, in person, Monday as the city ends remote work. Most will either need to be vaccinated, or undergo weekly Covid-19 testing to remain in their jobs.

The city was also set to start enforcing rules requiring workers and patrons to be vaccinated to go indoors at restaurants, museums, gyms and entertainment venues. The vaccination requirement has been in place for weeks, but had not previously been enforced.

There will also be a vaccine mandate — with no test-out option — for teachers, though they have been given until 27 September to get their first shot.

New York City kept schools open for most of the last school year, with some students doing a mix of remote and in-person instruction, but the majority of families chose all-remote learning. That choice won’t be available this year, Mayor Bill de Blasio has insisted.

“Our kids need to be in school and it’s unbelievable that some kids haven’t seen the inside of a classroom for a year and a half,” the mayor said on Thursday. “There are massive consequences to that, including health care consequences. The healthiest, best place for kids to be is in school.”

Masks will be required for all students and staff members, as is the case in schools across New York state.

There is no vaccine mandate for students 12 and over who are eligible for inoculations, but vaccinations will be required to participate in contact sports like football and basketball as well as some extracurricular activities like band practice and theater. About two-thirds of the city’s 12-to-17-year-olds are currently vaccinated.

De Blasio, a Democrat in his final months in office, has insisted that masks, cleaning protocols and random Covid-19 testing makes school buildings safe.

Asked if some students might just disappear from the system because their virus-wary parents won’t send them to school, de Blasio said “the vast, vast majority” of parents would bring their children to school.

“As a group, teachers have overwhelmingly supported the vaccine, but we have members with medical conditions or other reasons for declining vaccination,” UFT president Michael Mulgrew said in a news release.

Meanwhile, other unions for city workers have objected to the mayor’s decision to order employees back into workplaces, saying that if they were performing their jobs well remotely, they should be allowed to continue.