A former senior banker who is suing Merrill Lynch for £7.5m was "bullied and belittled" by her male boss, a tribunal in London has been told.
Ms Villalba was made redundant last August
Stephanie Villalba, who is claiming sexual discrimination, unfair dismissal and unequal pay, says she was eventually forced out of the firm.
If she wins the case the damages could be the biggest awarded by a UK employment tribunal.
It is the latest gender bias claim facing US bank Merrill Lynch.
The bank has already paid $100m (£53m) to settle nearly 900 claims in recent years.
Last month, it settled a 10-year battle with 1,000 female workers in the US who had claimed that the bank had a culture of bias against women.
And in April, the investment bank was ordered to pay $2.2m (£1.2m) in damages to Hydie Sumner, a female broker at its San Antonio, Texas office.
Based in the City, Stephanie Villalba worked for the bank's global private client business in Europe, investing funds for some of Merrill's most important customers.
But last August her employers told her she had no future in the company and she was made redundant.
The tribunal was told that while on one plane trip abroad with colleagues, Ms Villalba's male boss - Ausaf Abbas - told her to sit where the cabin crew sit and to serve drinks to the six male colleagues present.
Mr Abbas is also alleged to have described Ms Villalba as "high maintenance", and once when Ms Villalba said how hard she worked, he is said to have replied, "Stephanie my maid works hard".
Merrill Lynch denies Ms Villalba's claim and says she was removed from her post as head of the company's private client business in Europe because of the extensive losses the firm was suffering on the continent.
Nicholas Underhill, acting for Merrill, said it is "simply not the case" that Mr Abbas made the comments on the plane and that
the term "high maintenance" was not gender specific.
Mr Underhill said the maid comment was only meant to mean that "working hard is not enough".
He added that the decision to replace Ms Villalba was "a judgement based on her performance at that time,
it was nothing to do with sex".
The "evidence is overwhelming that she was doing badly" in this role, he added.
This case, which is scheduled to last for 30 days, could be particularly damaging to the investment bank as it threatens to uncover the US bank's most sensitive inner workings.
High-ranking Merrill Lynch executives are on standby to fly from New York to defend the bank at the tribunal in West Croydon.
They are likely to include Mrs Villalba's immediate boss, managing director Phil Sieg and his senior Raymundo Yu.