I received this today from the Foreign Office briefing service.
Information and travel advice during likely disruption on 24, 28 and 29 June. Industrial action by dock workers and airport staff has been announced for 24 June. All port and airport services are likely to be affected, including ferry services throughout Greece. Passengers are advised to contact the company they are travelling with for further information.
There is a possibility of a 48 hour general strike on 28 and 29 June. Further details will be confirmed as they become available.