Priti Dhulia, a tax consultant with Clifford Chance, has also alleged that her colleagues singled her out for making private phone calls in Gujarati rather than English.
The 54-year-old claims the experience at the so-called leading "Magic Circle" law firm has left her shattered, The Sunday Telegraph reported.
Ms Dhulia says she developed an adjustment disorder, went on to suffer severe depression and anxiety and was forced to take a year away from work.
"Its been a nightmare. They were out to get her. She was devoted to her work. She would be working at home until 2 am sometimes," her husband Viren told the newspaper.
According to a writ lodged with the UK High Court, she worked far longer than her contracted 35-hour week and was frequently forced to work at home in the evening and at weekends.
Ms Dhulia, from Hounslow in west London, worked for Clifford Chance from September 1995 to September 2015, during which she was promoted to tax consultant, preparing its partners Inland Revenue returns.
Ms Dhulia claims that over the years more and more work was assigned to her by her head of department, until she was carrying a far heavier workload than her colleagues.
Ms Dhulia's treatment is said to have worsened when colleagues began making snide remarks about the number of private phone calls she made, allegedly singling her out because some of them were in a foreign language.
She maintains her private calls were no more frequent than those of her colleagues in the same office.
Viren Dhulia, 57, who runs a stationery and art equipment shop, said: "It was ridiculous. My wife was speaking in Gujarati to her sister who was ill and had to have an emergency procedure. It was an urgent matter. Other people would make personal calls but because they were in English nobody cared."
In July 2011 his wife broke down in tears during an "assertiveness at work" course and complained she was being bullied, but says that no steps were taken to deal with the issue.
Three years later she was sacked after sending out a letter without consulting two senior colleagues, which was deemed to be seriously negligent.
Although her dismissal was rescinded just days later, she was left "constantly tearful, unable to sleep or eat, anxious and depressed" and her GP signed her off work with severe stress.
Priti Dhulia eventually resigned from Clifford Chance in September 2014.
A spokesperson for Clifford Chance said: "We disagree with the version of events presented in this case, however it would be inappropriate to comment further while legal proceedings are ongoing."