The UK House of Lords' EU Committee has stated that Bulgaria and Romania joined the EU "before they were ready" in 2007.
A group of peers argued that, when the two Balkan countries joined the bloc six years ago, agreed criteria which countries were supposed to meet before they can accede were not applied in full - meaning both countries joined without sufficient progress being made on judicial reform and corruption.
Corruption and judicial reform should have been tackled before they became members, the peers said, according to the BBC.
However, they noted that EU expansion had boosted economic growth and European security.
The committee also said that EU enlargement had become less of a priority given the ongoing economic difficulties in the Euro zone and there was a waning interest amongst aspiring countries.