"There is a strong possibility that the European Commission will open a phase two investigation although there is no final decision yet," said one of the people who declined to be named because of the sensitivity of the matter.
Another source said the companies have not provided concessions to the EU competition authority.
Read MoreGE offers conservative full-year guidance
Commission spokesman Ricardo Cardoso declined to comment. French industrial group Alstom could not be immediately reached for comment.
GE said it was cooperating with the Commission.
"Our goal is to secure the required regulatory approvals and close the transaction by mid-2015," the company said in an emailed statement.
GE has a checkered history with the Commission. Its planned takeover of U.S. industrial giant Honeywell was squashed by the EU watchdog in 2001 despite getting the green light from U.S. regulators.
Alstom shares were down by more than 1 pct after the Reuters story. They were trading 0.9 percent lower at 28.61 euros at 1552 GMT.
The EU competition authority is expected to announce the probe next week. Alstom, whose power assets contributed to more than two thirds of its revenues, wants to refocus on train-making after falling orders at its power turbines unit hit its cash flow and credit ratings.