How are the credentials of new MEPs verified? 

Newly-elected MEPs' credentials are verified to establish that they do not hold another office that is incompatible with membership of the European Parliament. Incompatible offices include being a member of government or of an EU member state parliament, the European Commission, the Court of Justice, the European Central Bank Board of Directors, the Court of Auditors, or the European Investment Bank. Active officials of EU institutions or bodies set up under the EU treaties to manage Community funds are also barred from being MEPs.

Once the election results are official, the Member States communicate the names of those who have won a seat to the EP and asks them to take the necessary measures to avoid any incompatibility of offices.

Before taking their seats, new MEPs whose election has been notified to Parliament must declare in writing that they do not hold any office incompatible with that of an MEP. This declaration needs to be made no later than six days before Parliament's constitutive sitting.

The new MEPs' credentials are checked ex post by Parliament's Legal Affairs Committee, which draws up a decision based on the information provided by the Member States. The decision is then passed to the President who informs the plenary during the next sitting. Other than checking the credentials, Parliament also rules on any disputes pursuant to the Act of 20 September 1976, except those based on national electoral laws.

Where it is established that an MEP holds an incompatible office, Parliament "shall establish that there is a vacancy."