Academy plans create unexpected allies
The teachers' unions say there's no hard evidence that making a school an academy is any guarantee of a better education for its pupils.
They also point to the lack of any reference to the scale of this change in the Conservative manifesto.
In local authorities where most of the schools are good, including some core Conservative heartlands, councillors are outraged at the prospect of no longer having a role in the quality of local education.
They're bridling at the implied criticism of their stewardship.
There is, says Christine Blower, general secretary of the National Union of Teachers, opposition that is "both very wide and very deep".
So what form might opposition take? Trade unions can consider industrial action but only on a legitimate trade dispute, not government policy.
If all schools become academies that would mean an end effectively to national pay scales, so that is where union opposition is likely to be located.
Conservative councillors will lobby MPs and the party leadership. Their influence lies in the ability to embarrass.
A very slender government majority among MPs, no majority in the Lords and a party fractious over the European Union aren't a recipe for making passing any legislation easy.
There is bound to be significant wrangling over amendments to any law to force schools down the road to becoming academies.
But there is no sign of any wavering from ministers. When I asked Schools Minister Nick Gibb this morning how he felt about opposition from within his party, he told me they were pressing ahead because in every area there are some schools that fall behind and that's not acceptable.
They want to break what they see as a monopoly of local authorities, to offer parents a choice between different brands of education from different chains of academy schools.
On Saturday, Nicky Morgan is likely to tell audience of teachers at the NASUWT teacher union conference that she, and the government, are not for turning on this issue.
And there is a thought provoking precedent. In the last Parliament, under a coalition government, the largest reorganisation of the National Health Service in living memory was carried out despite sustained and noisy opposition. The details had not been spelt out in the manifesto.
The difference maybe is that the issues in this case are easier for the public to grasp, particularly as for the moment thousands of parents are involved in sitting on the governing bodies of their local schools.
It takes something to unite union stalwarts with Tory leaders from the county shires.
But that's exactly what the plans to compel all state schools to become academies have done.