Teachers in Brookline, Massachusetts, are planning a one-day strike on Tuesday over issues with social distancing in classrooms.
Teachers say coronavirus rules need to be cemented down.
The teachers union says the district is reneging on its commitment to maintain six feet of social distancing inside school buildings.
The union says the superintendent now wants the ability to change the six feet requirement.
More on coronavirus
"What we don't want is one guy thinking he knows how the science should be interpreted," said Jessica Wender-Shubow, president of the Brookline Educators Union. "And it's going to affect thousands of other people."
The union has voted to go on strike to send a message.
Students won't be impacted, as Tuesday is a professional development day for teachers.
"This is about crowding the classrooms, it's about trying to get more and more kids into the room," said Wender-Shubow. "And that is dangerous."
In a statement, the district said, in part, that the superintendent "does not anticipate changing the six-foot distancing unless something significant happens to change our understanding of best practices … At any point before the end of the school year, the optimal mix of protective measures may be very different and less reliant on distancing."