"We are still looking at all the details," Commission spokesman Isaac Valero-Ladrón told reporters.
He said he could not give a publication date but that "the intention" was to disclose the proposals before the summer break.
EU Climate Commissioner Connie Hedegaard announced in April the Commission would bring forward a review of the carbon market, including changes to the auction timetable.
She said then the review should be published before the Commission's summer recess.
EU sources have said the draft proposals could delay the sale of either 400 million, 900 million or 1.2 billion carbon allowances in an attempt to tackle a huge surplus that has driven their price well below the levels needed to support low-carbon investment.
The Commission has declined to comment on detail prior to official publication, citing market sensitivity.
Changing the auction time-table could provide a quick solution.
Deeper structural changes to the ETS directive, which analysts say are needed to provide permanent support for the carbon market, would have to be decided through the full EU legislative process.