Rishi Sunak will strip some international students of the right to bring family members to the UK as ministers attempt to reduce net migration.
From January 2024 those studying in universities below PhD level will be barred from bringing their dependents, the Home Office announced on Tuesday.
It comes as the Government prepares to release figures on net migration from last year amid reports the figure could exceed 700,000.
The Prime Minister's official spokesperson claimed the changes were the "single biggest tightening measures a government has ever done" on migration.
The PM told Cabinet there had been an almost eight-fold increase in the number of family members visas issued - from 16,000 in 2019 to 136,000 in 2022.
In a statement, the under-fire Home Secretary Suella Braverman, who is facing calls to resign amid a row over a speeding ticket, announced the changes.
She said the new package will include "removing the right for international students to bring dependents unless they are on postgraduate courses currently designated as research programmes''.
The Cabinet minister said maintenance requirements for students and their dependents will be reviewed.
The changes will also remove the ability for international students to switch out of the student visa route into work before their studies have been completed.
"It's about getting the balance right," the PM's spokesperson said. "We have an extremely competitive offer to international students. That will remain.
"What we have seen is an unexpected consequence of our offer on dependence that there has been substantial growth. We think it's right to change that."
The release of net migration figures later this week also follows Mr Sunak backtracking away from the Tories' election pledge to reduce overall numbers.
At the time of the 2019 election, net migration stood at just over 250,000.
Mr Sunak could only say he wanted to bring "down legal migration" and declined to be drawn on whether he was committed to lowering it from 2019 levels.
He also appeared to blame his predecessors in No10, saying: "I've inherited some numbers, I want to bring the numbers down".
