The package, designed to help member states make the transition to a low carbon economy, will include eight legislative proposals that will shape EU energy policies beyond 2020.
Two of the draft laws concern the development of renewable energy and the redesign of the European electricity market.
It will be published by the Commission on Wednesday.
But, speaking at a news conference on Monday, environmental activists predicted that the long-awaited strategy, which is meant to underpin the EU's efforts to limit global temperature increase to 1.5 degrees Celsius, will "disregard" the Paris agreement and "fall well short" of what the EU needs to do to pull its weight in the fight against climate change.
By 2030, the EU has pledged to cut carbon emissions by 40 per cent, increase the share of renewable energy to at least 27 per cent and improve energy efficiency by at least 27 per cent.
Several groups - Greenpeace, Friends of the Earth Europe, WWF and Climate Action Network - have all voiced reservations about the package, which will run to some 500 pages and is seen as a milestone for EU energy policy.
These, they said, were based on leaked drafts of the package they had seen.
Among those expressing concern was Tara Connolly, Greenpeace EU energy policy adviser, who said, "From what we have seen, there are some good things and some bad things in the package.
"The Commission says it wants to put citizens at the heart of the energy union. This includes the right to sell and store electricity. We support increased energy rights for citizens so that is one of the good things."
She added, "However, there are some bad things in the package, such as plans to give new powers to local grid operators. This could create a conflict of interests and gives us real cause for concern."
Connolly added, "The Commission is making a lot of promises, saying it wants to be a world leader in tackling climate change and be the number one for renewables.
"But, at a time when the EU should be speeding up efforts to tackle climate change, we believe the EU is not moving fast enough and may, in fact, be even slowing down."
She added, "Europe will only meet its climate responsibilities if it enables its citizens to accelerate the transition to 100 per cent renewables."
Further comment came from Brook Riley, energy efficiency campaigner for Friends of the Earth Europe, who described the winter package as the "biggest" legislative dossier he had seen.
He pointed out that it will be subjected to up to two years of co-decision procedure before any final decisions are taken.
But he encouraged the Commission to increase the 2030 energy efficiency target from the proposed 27 per cent to 40 per cent, saying this would "lift millions of people out of energy poverty and cut greenhouse gas emissions."
Based on what she had seen, Imke Lubbeke, of WWF European policy office, described the package as "baffling."
She explained, "Less than a year since the Paris agreement and with investment in renewables in the EU falling behind the US and China, the Commission thinks now is the moment to weaken key elements of the EU's renewables energy framework and open the door to subsidies for old coal plants."
Her comments were endorsed by Jean-Francois Fauconnier, of CAN Europe, who predicted that the leaked proposals will "put the brakes" on the transition to a fully renewable energy system.