CHICAGO, USA (AP) — The Chicago Teachers Union said yesterday that its members voted to defy an order to return to the classroom over concerns about COVID-19, setting up a showdown with district officials who have said that refusing to return when ordered would amount to an illegal strike.

Chicago Public Schools (CPS), which is the nation’s third-largest district, wanted roughly 10,000 kindergarten through eighth-grade teachers and other staffers to return to school today to get ready to welcome back roughly 70,000 students for part-time in-school classes starting February 1. No return date has been set for high school students.

The teachers union, though, opposes the plan over concern for the health of its members and called on them to continue teaching from home – in defiance of the district’s plan. The union said the district’s safety plan falls short and that before teachers can return safely to schools, vaccinations would have to be more widespread and different metrics to measure infections would need to be in place.

“There’s no doubt we all want to return to in-person instruction. The issue is CPS’s current unpreparedness for a return to in-person instruction, and the clear and present danger that poses to the health of our families and school communities,” the union said in a statement.

The two sides have been negotiating for months, with talks continuing after the result of the vote was announced in the hopes of reaching a deal.

CPS officials said yesterday that they had agreed to delay the teachers’ return for two days to give the sides more time to negotiate. But they said K-8 teachers would still be expected to resume in-person instruction on February 1.

“We now agree on far more than we disagree, but our discussions remain ongoing and additional time is needed to reach a resolution,” the district’s CEO, Janice Jackson, said in a statement.

School officials have argued that remote learning isn’t working for all students, including many low-income and black and Latino students – who make up the majority of the district. The district’s safety plan includes thousands of air purifiers, more cleaning and a voluntary testing programme.

The roughly 355,000-student district, which turned to full-time online instruction last March because of the pandemic, has gradually welcomed students back. Thousands of pre-kindergarten and special education pupils resumed in-person learning earlier this month, and teachers who didn’t return to their classrooms were punished.