HONG KONG (Reuters) - Hong Kong’s top court on Monday began hearing the final appeal of a landmark LGBT rights case that has garnered public support from more than 30 top global banks and law firms, including Goldman Sachs and Morgan Stanley.

Marriage is legally defined as a monogamous union between a man and a woman in Hong Kong, where the lesbian, gay, bisexual and transgender community’s fight for legal rights has received support from multinational companies.

A British lesbian, known as QT, sued the director of immigration for denying her a spousal visa after her partner moved to the Chinese-ruled financial hub for work, even though they had entered into a civil partnership in Britain.

The government filed an appeal after QT won the case at the Court of Appeal in September.

The immigration policy was discriminatory as it placed gay couples at a significant disadvantage, QT’s lawyer, Dinah Rose, QC, told Hong Kong’s Court of Final Appeal.

“Every single gay couple is unable to comply with the policy,” she said.

It was “unprecedented” that so many private corporations applied to intervene in a human rights case, even though the court had dismissed their application, she added.

“The businesses are concerned the discriminatory way...is impeding their ability to recruit the best people, gay or straight, to work in Hong Kong, so Hong Kong can compete and thrive in an international market,” Rose said.

Hong Kong’s director of immigration was not obliged to recognize same-sex marriages because current Hong Kong laws do not do so, said Lord David Pannick, QC, representing the government.

“He may choose to go further than that, but he has no duty to do so,” Pannick, who appeared against the British government in the Article 50 Brexit case, told the panel of five Hong Kong judges.

Chief Justice Geoffrey Ma, however, said the immigration official’s principled approach on marriage was “inconsistent”, as some polygamous couples get exceptions, as well as same-sex spouses of consular staff.

“It does call into question…whether this sort of difference in treatment is actually right, whether it is fair,” Ma said.

Last week, a Hong Kong court ruled that the husband of a male civil servant was not entitled to spousal benefits, overturning a landmark lower court ruling in a setback for the city’s LGBT community.

There is no law against discrimination based on sexual orientation in the former British colony that returned to Chinese rule with wide-ranging autonomy, including a free judiciary, in 1997.