Anne-Marie Hutchinson, from Dawson Cornwell solicitors, has rescued hundreds of women and girls, sometimes as young as nine, from violent forced marriages and the risk of so-called honour killings in countries such as India, Pakistan and Bangladesh.
She also helps women in the Middle East and is one of the few specialists in the highly-complex area, which often involves securing international court orders restraining abusive partners from pursuing their victims.
Many of Miss Hutchinson's British clients contact her from abroad when they are trying to escape a forced marriage imposed by their parents or other relatives. Most cannot pay for her help and rely on legal aid.
But the firm has been told it is no longer eligible for legal aid funding to handle such cases. If the ruling is upheld on appeal, Miss Hutchinson's specialist practice, which has lasted more than 10 years, would end.
This decision prompted Olaf Henricson-Bell, joint head of the Foreign Office's forced marriages unit, which last year handled nearly 1,700 cases, to write a letter supporting Dawson Cornwell.
Sources with knowledge of the case say the decision to deny Miss Hutchinson's firm legal aid funding in this area stems from a decision by the Legal Services Commission in April to introduce a points-based system biased towards firms handling domestic proceedings in the family courts.
Miss Hutchinson's omission is described as an "oversight" and it is hoped the commission will reverse its ruling after an appeal, sources added. Shahien Taj, executive director of the Henna Foundation which helps women to escape forced marriages, said the ruling was "bonkers".
The Legal Services Commission said it would look at appeals on a case by case basis.