The trade union Verdi has called for a three-day nationwide strike of Lufthansa ground staff starting from Wednesday as a wage dispute with the German flag carrier escalates. The union has already held two one-day strikes this month. The most recent action by technicians, logistics and counter staff was on February 20, when Lufthansa was forced to cancel 90% of its flights. The strikes crippled Lufthansa operations at its hubs in Munich and Frankfurt, but flights were also cancelled at many other airports. After previous rounds of negotiations, Verdi recently rejected as insufficient another o…