German news ticker was saying last night it was a 'warnstreik' lasting three hours from 0615 at Frankfurt.
From the Lufthansa website:
Warning Strike at Frankfurt airport The cabin crew union 'UFO' has announced a warning strike for today, Friday 23rd January 2009 from 06:15 - 09:15 local time at Frankfurt airport. Lufthansa is doing its utmost possible to reduce the impact on flight operations. However irregularities on domestic and continental routes to or from Frankfurt might be unavoidable. The intercontinental traffic is expected to operate regularly.