The Turnbull government will invest an extra $1.2 billion in schools but seek to impose new conditions on the states and territories to get the money.

The new funding to be unveiled by federal Education Minister Simon Birmingham on Sunday falls more than $3 billion short of what was promised under Labor's Gonski school reforms, setting the scene for a major election campaign fight with state governments and teachers.

The money will be part of a $73.6 billion schools package to be included in Treasurer Scott Morrison's first budget on Tuesday, Fairfax Media can reveal.

The $1.2 billion increase will be spread over 2018, 2019 and 2020 – the final two years of the Gonski plan, plus an extra year.