The amicus brief is a joint effort between Google, Levi Strauss & Co, the San Francisco Chamber of Commerce and automated document review company H5.

As reported in itnews.com.au, Google, which has its head office located in California, has claimed that it has many gay and lesbian employees who came to work for the company when gay marriage was legal. If these marriages were annulled as a result of the proposition, Google argues that it could lose these employees, placing it at a commercial disadvantage.

The company also claims that the proposition will greatly disrupt its internal payment systems, resulting in significant costs, because health insurance, tax benefits and taxation systems based on gay marriage being legal will need to be adjusted.

Proposition 8, which was passed by a narrow majority in the Californian general election last November, effectively over-ruled the decision in In re Marriage Cases (2008) 43 Cal.4th 757 which confirmed the legality of gay marriages last May. Since then, a number of groups and individuals have brought legal actions challenging the proposition's constitutionality.

Google has publicly opposed Proposition 8 for some time. A message on its official blog from September last year reads: "It is the chilling and discriminatory effect of the proposition on many of our employees that brings Google to publicly oppose Proposition 8. While we respect the strongly held beliefs that people have on both sides of this argument, we see this fundamentally as an issue of equality".

In a further post last week, Google's general counsel, Kent Walker, said that the company is concerned about the impact the proposition could have on the state's ability to attract and retain "a diverse mix of employees from around the world". "Denying employees basic rights isn't right, and it isn't good for business," Walker said.