The country’s largest cable company has joined the race to get skinny.

Comcast has started ripping up agreements with cable networks and moving them out of basic onto digital tiers, The Post has learned.

Already, Spike, CMT and Pop, the former TV Guide channel, have been moved to digital tiers, the companies told The Post.

The switches began Jan. 7.

The changes mean fans of the affected networks could have to pay $9.99 a month, or more, to tune in.

It also means the affected networks will have a less broad reach.

Comcast said the moves are aimed at keeping down costs for its customers, but at least one company — Spike- and CMT-owner Viacom — is irked by the move.

“This action is in direct violation of our agreement and will increase costs for customers who will now have to pay more for networks that were previously included in less expensive packages,” Viacom said in a statement.

The media conglomerate, which owns a dozen entertainment brands, including MTV, Comedy Central and Nickelodeon, in addition to the networks switched by Comcast, wants customers to know the extra fees go into Comcast’s pocket — not theirs.

“We continue to address our concerns directly with Comcast and hope their customers will do so as well,” the statement said.

Channel shifting is common practice in cable-land — but has become a more tense affair as distributors like Comcast move networks to digital tiers to shrink the lineup, and cost, of basic cable.

The moves hope to staunch cord-cutting.

Disney remains embroiled in a legal battle with Verizon Fios after the pay TV company shifted ESPN out of its basic package last April.

‘Due to increasing programming costs, we sometimes need to make adjustments to our channel lineup.’ - Comcast

Disney’s ESPN has lost 7 million homes since 2013, according to several reports, as customers look to cut costs.

Subscriber counts are under the microscope on Wall Street as investors weigh how resilient the pay-TV sector is.

Comcast said the changes are aimed at providing customers bang for their buck.

“Our goal is to provide customers with the best value and most viewing choices,” Comcast said. “However, due to increasing programming costs, we sometimes need to make adjustments to our channel lineup.”

Moves to get skinny — or less expensive — may be working.

Research firm MoffettNathanson noted that cable just had its best year in a decade while slowing programming expense growth.

“Cable will end [2015] with a loss of approximately 514,000 subscribers,” telecom analyst Craig Moffett wrote in a Jan. 13 report, but that was less than half the loss of 2014.