Environement charity WWF made the call ahead of an Energy Council meeting in Luxembourg on 11 June.
Ministers are expected to finalise their position on clean energy laws including the renewable energy directive and energy efficiency directive and their 2030 targets.
The European Parliament has backed a 2030 renewable energy target of 35%, while the EU Council offered to back a target of 30-31% or 32-33%, depending on the degree to which parliamentary negotiators are prepared to cave in to those demands.
"Having started off on the wrong foot, with weak positions on renewables and energy efficiency, member states now have a chance to shuffle forward in the Parliament’s direction," Imke Lübbeke, head of climate and energy at WWF Europe.
Lübbeke said that ministers from France, Germany, the Netherlands, Sweden, Finland, Portugal and Luxembourg have already spoken out in favour of higher ambition and urged them to "stand up and stand firm" to back high ambitious green targets.
The Parliament’s rapporteur on the energy efficiency file, Miroslav Poche, of the S&D group, urged member states that have shown willingness to increase the ambition of the target to "take a stand".
Pierre Tardieu, chief policy officer at trade body WindEurope, said there was clear political direction for a 35% renewable energy target due to new governments in Spain and Italy that could "put their weight behind an ambitious target".
Trilogue negotiations between the Parliament, the Council and the European Commission on the EU’s clean energy laws are set to conclude on 13 June.
However, it is not clear whether a final deal will be reached by the end of the Bulgarian presidency, which ends on 30 June.