Mass strike action on Wednesday will cause "significant disruption", Downing Street has said.
Teachers, university workers, civil servants, train and bus drivers are all due to walkout during the day.
Around 500,000 workers are due to take part, making it the biggest strike in more than a decade, according to the Trades Union Congress (TUC).
Talks between teaching unions and the Department for Education (DfE) ended without progress on Monday.
The National Education Union (NEU) said Education Secretary Gillian Keegan had "squandered an opportunity" to avoid Wednesday's strike action.
