Environment Commissioner Janez Potocnik recommended the European Commission send Poland its first warning and Belgium its second warning on air pollution.
European law calls on member states to be in line with rules that aim to reduce fine particulates in the air. Fine dust particles released by machines ranging from diesel-powered vehicles to household boilers have a negative effect on human health and the environment.
Poland and Belgium, the European Commission said, haven't transposed into national law European rules on air pollutants.
The European Commission called on Poland to implement the measures in July. Belgium was called on first in November 2009 and again in June to adopt the legislation.
"Both member states have two months to comply," the European Commission said in a statement. "Failing this, the commission could refer the cases to the European Court of Justice."