GroupM Canada says barring Canadian TV broadcasters from airing Canadian advertising with shows from the United States would dramatically cut revenues.
And at least one major corporate player, BCE, says the practice should be expanded, not eliminated.
The statements came as the Canadian Radio-television and Telecommunications Commission enters a third day of hearings into the future of TV.
GroupM chief commercial officer Stuart Garvie says the end of so-called simultaneous substitution would mean Canadian broadcasters could no longer afford to air TV shows and events from south of the border.
The CRTC has proposed new regulations that would, if enacted, forbid TV stations from replacing U.S. advertising with Canadian spots on American shows.
The practice has frustrated Canadian viewers, particularly during major sporting events, when they are unable to see the ads that American watchers see, such as during the Super Bowl.
The CRTC stresses that the proposals are merely a guideline up for debate during the hearings.
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"We believe that the proposals put forward will have serious negative impact on the media and marketing industries in Canada, leading to significant job losses," he said.
BCE and Bell Canada executive Mirko Bibic told the hearings that local stations, not just the big networks, should be allowed to simultaneously broadcast Canadian advertising while airing U.S. content.
"We need to not only maintain simultaneous substitution but should convert to a local specialty model and improve the protection of the Canadian rights market," said Bibic.
The regulator has also proposed, among other things, that consumers be allowed to pick the individual channels they want from cable and satellite service providers, over and above a price-capped, trimmed-down mandatory service that includes mainly local channels.
The so-called “pick-and-pay” option would cost between $20 and $30 a month, as outlined in proposals put forward by the CRTC in August.
Bibic said BCE, which owns CTV, Bell and a number of local TV stations, accepts that cable and satellite programming should be "unbundled."
But he says complete unbundling beyond so-called "skinny basic" packaging would threaten the ability of TV networks and stations to create high-quality Canadian shows.