Teachers in Nottingham are threatening to intensify their strike action over changes to the school year by staging as many as three walkouts in one week.
ITV Central has learned that the National Union of Teachers (NUT) is consulting members about further stoppages.
It comes after a meeting on Wednesday between regional NUT officials and Nottingham City Council ended without progress.
The union offered to set up talks with national officials, but Councillor David Mellen, the council's Portfolio Holder for Children's Services, says he declined as he did not wish to take a local dispute to national level.
The council wants to introduce a five-term year from September 2013 with a shorter four-week summer holiday.
It claims the changes would improve pupils' learning and attendance.
But critics say the terms will be too long, children need a six-week break in the summer, and fear chaos as Nottingham's holidays would be out of step with neighbouring local authorities.
The NUT has already staged two one-day strikes, affecting thousands of children in the city.
The last, on Tuesday, closed 18 schools and affected another 36.
The next walkout is due to take place on Wednesday.
But the NUT has told ITV Central it's considering escalating the action to strikes of two or three days in a single school week during the current summer term.