Rules for staying in the Schengen zone do not apply to the citizens of the European Union. Every time when you enter a member country, a new three month free residence period begins.
EU citizens' passports are not stamped when crossing borders between member states. Official identity cards can also be used as a valid travel document. Please note, however, that a driver's licence is not an acceptable travel document.
In accordance with the EU decision Finland has cancelled the visa regime for non-citizens residing permanently in the new EU member countries and travelling with the documents issued by these countries. But, non-citizens going to Finland to work will still need to apply for a residence permit for work. Please also note that only the employee himself/herself can initiate this application process. For further information, please read the section Residence permit and the Finnish Immigration Service's homepage.