Both government and parliament said the two countries are too corrupt and fail to live up to the rule of law, a precondition for accession.
Finland’s objection is backed up by fellow Schengen member Germany.
Interior minister Päivi Räsänen rejected claims that Finland's stance is coloured by the persistent problem of eastern European Roma beggars in Finnish cities.
Räsänen said Romania and Bulgaria were too easily allowed into the 27-member bloc in the first place.
"Too many questions were left unanswered which we now have to deal with," she said.
Finland has previously stated that it worries that corruption would prevent the countries from properly securing the outer borders of the EU.