Public service union Unison says such staff are often not being paid full sick pay by private companies contracted to work in schools.
And it says it is compiling a list of those companies, which already includes several large contractors each with contracts in hundreds of schools.
“That means some people could still be going into schools when they’re ill or have the virus, which will spread infections more widely.
“We’re currently taking a close look at school contractors and will be urging any still granting just statutory sick pay to affected individuals to change their policy. We already know of several large contractors denying staff full sick pay, and they each have contracts with hundreds of schools.
“Some of the big MATs are saying they’ll make sure their contractors do the right thing, and that they’ll review contracts if they don’t. Good on them.”
Last month, Unison was among the unions that wrote to education secretary Gavin Williamson calling for extra measures to halt rising infections in schools, including full pay for lower-paid workers who need to isolate.
The unions, including GMB and Unite, which together represent teaching assistants, technicians, catering workers, cleaning staff, caretakers and receptionists, also called on the government to make it clear whether these staff members are a priority for testing like teachers.
The DfE has been contacted for comment.