The European Union is planning to pressure the United States to include all EU Nationals (27 member states) in its visa-waiver program. EU is insisting that the visa-waiver be fully reciprocal since all EU member states allow US citizens to enter without visas.

"U.S. officials say Greece and most of the newer EU members still fail to meet criteria for joining the visa-waiver program."

I am guessing that...

When the U.S. signed the reciprocity agreement, they only had the initial 15 member states in mind.

If it was up to me...

I would not agree to full reciprocity unless the newer members have met the criteria set by the U.S. Yes, despite the fact that these countries are now EU member states. The fact that Slovenia -- a new member -- enjoys U.S. visa-waiver benefits whereas Czech Republic, Greece and Slovakia do not, should say a lot.

Besides...

Shouldn't EU understand the concerns of the U.S.? After all, they also have the same problems with illegal migrants or overstaying "tourists".

EU has argued that U.S. citizens are enjoying visa-waiver in ALL EU member states hence, they should reciprocate. Rigghhht... but I do not see a deluge of US citizens in danger of overstaying or illegally migrating to those countries, either.

My two cents.