A group of 16 international law firms from the United States, Europe and Asia, including Latham & Watkins, Davis Polk & Wardwell and Clifford Chance, have joined forces as they seek to join a lawsuit in Hong Kong on behalf of a British lesbian in a landmark case that will decide whether spousal dependents in same-sex couples can obtain visas to reside with their partners in Hong Kong.

The law firms, along with 15 foreign banks and Amnesty International, are urging the Hong Kong Court of Final Appeal—Hong Kong’s highest court—to uphold a lower court’s decision to allow spousal dependent visas for same-sex couples.

“The 16 law firms represent a cross-section of employers within the Hong Kong legal services industry,” Davis Polk said in a statement. The firm is acting pro bono on behalf of the law firms on the case, along with a team led by Hong Kong-based counsel Chen Zhu.

“These law firms also share a commitment to promoting LGBT diversity and inclusion within their respective firms and the legal profession more broadly,” the statement said.

The participating U.S. firms are Akin Gump Strauss Hauer & Feld, Hogan Lovells, Latham & Watkins, Morrison & Foerster, Paul, Weiss, Rifkind, Wharton & Garrison and Ropes & Gray. Four Magic Circle firms Clifford Chance, Linklaters, Allen & Overy and Freshfields Bruckhaus Deringer signed the petition. Ashurst, CMS, Eversheds Sutherland, Herbert Smith Freehills, and Hong Kong firms Morley Chow Seto; and Oldham, Li & Nie are also part of the group.

The case in question started in 2014 when a female British national who court documents referred to as QT was denied a visa to remain in Hong Kong as a spousal dependant of her partner,  who the courts refer to as SS. QT and SS had entered a civil partnership in the United Kingdom prior to moving to Hong Kong for SS’s work in 2011.

The Hong Kong Immigration Department denied the visa on the ground that QT wasn’t a “spouse” to SS as the government’s existing policy defined spouse based on “monogamy and the concept of a married couple consisting of one male and one female.”

QT then filed for a judicial review against the department’s decision but lost in 2016 when the High Court ruled in the government’s favor. She appealed and won before the Court of Appeal last September when a three-judge panel agreed that QT suffered discrimination based on her sexual orientation. The government appealed again to the Court of Final Appeal; a hearing will be held June 5.

Hong Kong-based law firm Vidler & Co. represents QT in the case and first disclosed the law firms’ petition to intervene last week in a Facebook post.

“[The law firms] seek to highlight the significant burdens and challenges that the Immigration Department’s policy imposes on both employers and employees in the legal sector,” said Davis Polk’s statement.

“The [Immigration Department's policy] significantly diminishes their ability to attract and retain the world-class talent that is crucial to maintaining and enhancing Hong Kong’s status as a leading legal services center in Asia Pacific and globally.”

If the Court of Final Appeal approves the application to intervene, the law firms will be able to present written arguments before a five-judge panel. A dozen foreign banks attempted to intervene in a similar manner when the case was before the Court of Appeal last year; their application was denied.