The UK's Competition and Markets Authority (CMA) has extended its Phase 2 probe into Vodafone and Three's proposed £15 billion ($19bn) merger.
It means that the decision is now set to be made on December 7.
Initially, the deadline for a decision was September 18, before being pushed back to October 12, a month later.
The UK’s next big telco merger - Vodafone and Three?
Will four become three in the UK? Advanced talks between Vodafone and Three have got the industry talking about a potential merger and its chances of success.
The CMA launched its Phase 2 investigation into the merger, which is poised to create the UK's biggest mobile network operator, back in April.
"The Inquiry Group now considers that it will not be possible to complete the investigation and to publish its final report within the revised reference period," the said CMA last week.
The regulator added that it needed to fully "assess the implications" of the recently announced network-sharing agreement signed by Virgin Media O2 and Vodafone.
It kicked off the Phase 2 investigation around a month after it had voiced concerns that the merger would lessen competition in the UK telco market, following a 40-day review.
If approved, the deal means that the UK will go from having four mobile network operators to three.
The merger will give Vodafone a 51 percent majority stake in the combined entity, currently labeled as "MergeCo," with CK Hutchison's Three holding the remaining 49 percent.
Both telcos have previously welcomed a more in-depth probe into the proposed union.
"I don’t think the delay will have much bearing on the eventual outcome," said Kester Mann, director of consumer and connectivity, at CCS Insight.
"We already knew it is a complex case with wide-reaching implications and that there are significant regulatory concerns."
