EU competition regulators will tell Three Ireland’s parent company that its bid to buy O2 Ireland might be problematic unless it offers concessions, according to sources.

The European Commission opened an in-depth investigation into Hutchison Whampoa’s €780 million bid for O2 Ireland two months ago and will send a statement of objections laying out its concerns this week, the sources said.

Regulatory reviews of the Irish merger and another in Germany where Telefonica Deutschland is seeking to buy Dutch group KPN's local unit E-Plus, are seen as critical for the mobile industry in determining whether the European Commission will allow deals which reduce the number of players in a national market.

"It shows the Commission getting tough on three to four deals," one of the people said.

"Hutchison will be offering concrete remedies once it receives the statement of objections," the person said.

The acquisition of O2 Ireland would quadruple Hutchison's share of the market to 37.5%, behind market leader Vodafone's 39.4% but ahead of rival Meteor's 19.7%.

Commission spokesman Antoine Colombani, declined to comment.

The EU watchdog has set a 24 April deadline for its decision.

It can extend the review depending on when Hutchison submits concessions.

The company can request an oral hearing in front of senior Commission officials to argue its case.

Last year Hutchison's Austrian unit won EU regulatory approval for its acquisition of Orange Austria from France Telecom only after agreeing to divest some radio spectrum and making it easier for rivals to access its network.