Firms should allow parents to bring their children to work during next week's strike, Prime Minister David Cameron said as he indicated he might be willing to make it harder to take industrial action.
Millions of parents are expected to struggle with childcare as teachers strike next Wednesday, a move which could lead to the closure of thousands of schools.
As he urged bosses to allow their staff to bring children to work, Mr Cameron hit out at Labour's links to the unions, saying the proportion of the party's funding from the unions since Ed Miliband took over as leader had risen from 56% to 86%.
There were calls of "change the law" from the Tory benches after senior Tory MP Richard Ottaway said strikes should be banned unless 50% or more of a membership vote for it.
Speaking during Prime Minister's Questions, Mr Cameron replied: "It is wrong that these strikes are going ahead when these negotiations are under way, it is wrong to strike and close so many classrooms and essential services, but it is being done on the basis on these turnouts.
"Just one quarter of Unison members voted to strike, just 23% of those balloted at Unite voted in favour. I am not surprised Labour members want to shout me down. We know why they won't condemn the strikes because we have got the figures today from where they get the money from.
"In his first year as leader of the party, 86% of Labour's donations have come from the trade unions. Under the last Labour leader it was 56%. Is that the only thing you have improved since the time of Gordon Brown?"
Asked about whether they were considering changes to the law, No 10 aides said "We are not at that stage", adding: "It is never off the table."
A source indicated that No 10 staff could be among those who were able to bring their children to work.
She said: "Downing Street would be one of the places where if you want to bring your children, that could be arranged."