Salt Mobile, which is owned by French billionaire Xavier Niel and operates in Switzerland, believes the deal may violate terms of a now-paused $3.1 billion broadband joint venture, called Swiss Open Fibre, that Salt and Sunrise had announced in May.
Sunrise's board unanimously approved the Liberty Global takeover announced this month and Sunrise shareholder Freenet of Germany has tendered its 24.4% stake, steps which Salt contends "have already destroyed significant value for Salt and its shareholders".
"Salt is concerned that the proposed transaction...infringes on contractual rights established as part of its Swiss Open Fibre joint venture with Sunrise," Salt said in a statement.
Sunrise countered that it has not violated any contractual obligations to Salt and that nothing about the Salt-Sunrise tie-up in May precluded a tender offer like Liberty's.
"This scenario of an unsolicited tender offer was explicitly catered for in the agreement between Sunrise and Salt," Sunrise said in a statement.
"Sunrise has at no time solicited or encouraged Liberty's offer," Sunrise said.
"Indeed, Sunrise rejected Liberty's first proposals...Only once the current offer was proposed by Liberty, the Sunrise board of directors determined that it was in the best interest of the company."
No lawsuit has yet been filed, Sunrise added.
Quinn Emanuel Urquhart & Sullivan, LLP is representing Salt and filed paperwork in a U.S. court to allow it to gather evidence for use in a non-US case.
The Financial Times first reported Salt's lawsuit threat.
(Reporting by John Miller; Editing by Keith Weir)
