The throttling has begun in earnest. According to a report from Bloomberg based on a study from Northeastern University and the University of Massachusetts, telecom companies have taken advantage of the end of net neutrality to begin slowing delivery of video and data.

If the practice continues and expands, it could cause consumers to watch or finish less video. In that case, completions and ad exposures might be affected. That’s the immediate implication for marketers and why they should be concerned.

The Federal Communications Commission (FCC) passed net neutrality in 2015 during the Obama administration. The Republican-controlled FCC formally abolished it in June.

Netflix and YouTube so far have been the primary targets of the telecoms:

Among U.S. wireless carriers, YouTube is the No. 1 target of throttling, where data speeds are slowed, according to the data. Netflix Inc.’s video streaming service, Amazon.com Inc.’s Prime Video and the NBC Sports app have been degraded in similar ways, according to David Choffnes, one of the study’s authors who developed the Wehe app.

All the major wireless carriers are doing this, according to the study, with AT&T and Verizon being the biggest throttlers. The carriers have defended their actions as traffic management and not “throttling.”

Recently, during the largest wildfire in California history, Verizon was accused of limiting data speeds of California firefighters, forcing them to pay more for data. Verizon later claimed it was a customer service-related mistake.

Last month, over the objection of telecom lobbyists, the California legislature passed a law that restores net neutrality for California residents. Similar initiatives have passed or are proposed in other states. The California bill prevents internet service providers from blocking or slowing traffic or extracting payments from content publishers for “fast lanes.”

The bill still needs to be signed by California Governor Jerry Brown to go into effect. It’s a near certainty that ISPs/telecoms will litigate to block the California law and other state net neutrality initiatives.