Sky Network Television said the date for a decision on its application to merge with Vodafone New Zealand has been pushed back to the week before Christmas to let the Commerce Commission process new submissions.

The commission's decision had been due on Friday, but is now expected to deliver it on December 21, according to the broadcaster.

Sky TV's shares have dropped 15 per cent in the past month and last traded at $4.24.

On October 31 the commission said it was in talks with the companies to extend the application timeframe to give them the opportunity to submit on its initial view.

At that stage, the regulator wasn't satisfied the deal wouldn't substantially reduce competition, saying while consumers may benefit from cheap services at first, other broadband and mobile providers could lose the ability to build scale in their businesses and become weaker rivals.

The merged business would also face weak incentives to ensure Sky's services were available to rivals on competitive terms.

Spark New Zealand and Two Degrees Mobile have formally opposed the merger, saying the deal would adversely impact consumers as a result of creating a company willing and able to use premium live sports content to stifle competition.

"The commission continues to take an appropriately thorough approach to this transaction and Sky will continue to provide any additional information sought by the commission as swiftly as possible," Sky said.