The EU wants to launch a multi-billion-euro Just Transition Fund with cash from the bloc's coronavirus recovery fund and budget, to help fossil fuel dependent regions shift to cleaner energy.
The goal is to push members towards EU goal of net zero emissions by 2050, and a new, tougher 2030 target for emission cuts, which the EU Commission proposed this week.
But final rules need to be decided by the European Parliament together with the Commission and national governments, which have said the fund should not support any fossil fuels.
The parliament on Tuesday voted to back an amendment to make some gas projects eligible for aid and will formally approve its position with another vote on Wednesday. The projects must be in coal-heavy regions and comply with the EU's 2030 climate target.
Greece's Manolis Kefalogiannis, lead lawmaker on the issue, said the rules enabled a "limited possibility of investments in natural gas as a 'bridging fuel'".
Others said spending public money on gas contradicted EU lawmakers' promise, made last year, to tackle the "climate emergency".
"It's just not explainable to the public," said German Green party lawmaker Niklas Nienass.
Gas emits roughly 50% less CO2 than coal when burned in power plants, but it is also associated with leaks of methane, a potent greenhouse gas.
The EU parliament also said countries should only get Just Transition Fund money if they pledge to become climate neutral by 2050 - a condition aimed at Poland, the only country that has not signed up to an EU-wide goal to become climate neutral by that date.
By Kate Abnett