Vodafone will receive a warning from EU regulators about possible anti-competitive effects from its $22 billion deal to buy Liberty Global's German and eastern European assets.
This is according to two people familiar with the matter.
The warning, via a statement of objections setting out the European Commission's concerns, is expected to be conveyed to the companies shortly, the sources said.
This comes ahead of a June 3 deadline for the EU executive's regulatory approval.
The world's second-largest mobile operator and US cable pioneer John Malone's Liberty announced the deal in May last year in a move that would help Vodafone to compete with rival Deutsche Telekom in its home market.
Commission spokesman Ricardo Cardoso and Vodafone declined to comment.
The EU competition enforcer opened a full-scale investigation in December last year, saying that the deal could hurt competition in Germany and the Czech Republic.
Vodafone is expected to offer concessions to address EU concerns about the deal.