Conservative Party leadership hopeful Sajid Javid has been accused of “human fly-tipping” over his decision to revoke the citizenship of Islamic State bride Shamima Begum.
A lawyer representing the family of Ms Begum has called for the home secretary to reverse the decision and offer an apology.
Mohammed Akunjee has accused Mr Javid of using the case to further his political career.
In a letter, he wrote: "Your act represents the most profoundly egregious, capricious and politically-driven abuse of power.”
The home secretary cancelled the teenager’s British citizenship in February; four years after Ms Begum joined the extremist group.
The 19-year-old was 15 when she and two other schoolgirls left Bethnal Green in east London to join Islamic State.
She resurfaced earlier this year in a Syrian refugee camp, heavily pregnant and seeking to return home.
Her baby, named Jarrah, was born on February 16 and died three weeks later. He was her third baby to die in Syria.
Mr Akunjee has said the decision to revoke citizenship was illegal under international law.
It was thought Ms Begum was eligible for Bangladeshi citizenship due to her family background, but this has been denied by Bangladeshi officials.
It effectively leaves Ms Begum stateless and unable to leave Syria.
Mr Akunjee said “Shamima Begum's parents never contemplated a life for her in Bangladesh.”
“Rather than take responsibility for Shamima Begum and her son, you took a British problem and illegally dumped it on our innocent international neighbours.”
He added: “Shamima was born, raised, groomed and radicalised here in the UK.”
The Home Office said it did not routinely comment in individual cases.