The European Union's competition commissioner has expressed doubts about Hutchison 3G's €1.3 billion bid for France Telecom's Orange Austria.
Joaquin Almunia said Hutchison 3G - Austria's third-largest mobile operator - may not be able to offer sufficient concessions to satisfy regulators.
Almunia commented that the deal, if approved, "would bring the current four competitors in the national mobile market down to three".
Hutchison 3G is a division of Hutchison Whampoa, controlled by Hong Kong billionaire Li Ka-shing.
It has offered to let rivals use its mobile network to ease concerns about the elimination of a fourth player, but some rivals were sceptical about the proposal when asked by the commission.
Almunia was making a speech at the Georgetown Law School in Washington, USA.
He added: "We are looking very carefully into this proposed merger and we have recently raised objections against it. At this stage, the question remains whether effective remedies will be found to clear this merger."
Hutchison 3G's bid has faced previous opposition from Austria's Federal Competition Authority.