Spark managing director Simon Moutter has fired a shot at Sky TV while plugging his own company on Twitter.
Moutter posted a photo of him smiling as he put a Sky TV set-top box and remote in a packaging box, saying he was sending the device back.
"Sending my box back to Sky TV. So much better value with Lightbox and other on demand streaming services nowadays," he captioned the photo.
Asked about Moutter's claim, Sky's director of communication Kirsty Way said the Spark boss clearly wanted to promote the "business he is in and encourage more people to get his streaming service for free".
"Personally I think he'll find much better and much more entertainment on NEON (including movies and HBO!!) if he wants to save some money. Perhaps he doesn't love sport like so many of us kiwis do or perhaps he does and is loving FAN PASS?," she said.
NEON is Sky's online television and movie service while FAN PASS livestreams sports to computers and other devices.
Spark's biggest competitor in the telecommunication space Vodafone is hoping to merge with Sky TV in a proposal that is currently before the Commerce Commission.
Spark filed a submission to the Commission saying the merged entity would hurt sports fan's access to sport broadcasts.
The submission said if the Commission rejected the proposed merger then market pressures on Sky TV would force it to make all sports content available online and on-demand.
"We believe if the Commerce Commission blocked the proposed merger, Sky would be forced by commercial realities to make all of its sports content available online and on-demand," Spark said.
Sky and Vodafone have previously said they would respond to all submissions against the proposed merger in a formal response to the Commission.
Last week Spark announced head of Lightbox, Kym Niblock, would leave the position at the end of the year.
The streaming service has been bundled into broadband packages offered by Spark and would become free for customers who have a pay-monthly mobile plan.
The service was launched in August 2014 with a price of $15 per 30 days, following an initial free trial 30 days. It preceded the arrival of its American rival, Netflix, which launched in March 2015, and led to Lightbox lowering its price to $12.99 to match its new rival.