Swatch and Tiffany sue each other over partnership
Swatch and Tiffany are suing each other following the collapse of their production deal.
In 2007, Swatch agreed to produce watches under the Tiffany brand. Under the deal the two firms would have shared the profits.
But last year Swatch ended the deal, accusing Tiffany of blocking the development of the business.
Swatch is now suing Tiffany for 3.8bn Swiss francs ($4.1bn; £2.6bn), and Tiffany has launched a counterclaim.
Tiffany is claiming 542m Swiss francs in compensation.
Swiss group Swatch says it will "vigorously contest" that claim.
It invested millions to develop the watches and planned to sell them through its own chain of stores as well as Tiffany jewellery shops.
But Swatch said Tiffany appeared to lose interest in the business and blocked its development.
Swatch terminated the agreement with the US jewellery retailer last year.
In response Tiffany said that it had "honoured its obligations under the agreement".