With the task of measuring TV viewing growing ever more complex, CBS is actively considering cutting ties with Nielsen as the companies negotiate a renewal of their long-term contract.

The current deal, worth about $100 million, is set to expire on December 31.

Sources familiar with the CBS perspective said the most-watched network is chafing at the steadily increasing rates Nielsen is charging given the difficulty of accurately capturing viewing across linear TV and digital platforms. CBS has generally taken a more low-key approach than that of companies like NBCUniversal, Fox, Turner and Viacom, which have openly criticized Nielsen and rolled out self-generated data offerings as a replacement.

CBS declined to comment on the situation, which first surfaced in a report by Variety.

In a statement, a Nielsen spokesperson said, “We expect to arrive at a mutually beneficial agreement well in advance of December 31.”

Despite getting the most eyeballs overall regularly among the Big 4, CBS execs have long expressed frustration with Nielsen and its emphasis on the 18-49 demo and overnight results. A source inside the network said on both a local and national level, the company feels it is being compromised by “monopolistic behavior” by Nielsen. “We’re paying more and getting less,” the source said. “They’re just not able to deliver a picture of this new world.”

Other options would include signing a deal with comScore, a much smaller rival, or providing clients with data from whatever CBS can collect. The very existence of Nielsen, though, is due to the perception among advertisers of networks “grading their own homework,” so a third-party solution has always been accepted as a necessary part of the TV landscape. Even so, as the business has evolved from three broadcast networks to cable, digital and social, with most viewing now time-shifted, the game of chess has become multi-dimensional.

Grousing about Nielsen is akin to shooting fish in a barrel, though a major network threatening to outright drop the service is not exactly par for the course. NBC took a firm line with Nielsen a couple of years ago, publicly admonishing it for its multi-platform ratings tools and then shedding the service for non-prime hours on its business network CNBC, which is widely viewed outside the home.

The spilling over of tensions into public view is an unusual turn of events for two companies who are among the most venerable and deep-rooted in all of broadcasting. The snag is also occurring as David Poltrack, the Chief Research Officer at CBS and the longtime dean of network researchers and ratings experts, plans to retire in June 2019.

Radha Subramanyam, Executive Vice President, Chief Research and Analytics Officer, is overseeing research as Poltrack makes his transition. Subramanyam is a former executive at Nielsen.

Dominic Patten contributed to this report.