Uh oh. Looks like advertising for Sprint’s “Cut Your Bill in Half” promotion is on the chopping block.

The National Advertising Division (NAD) recommended Sprint end airing of its Half Off commercials and tweak its Internet and in-store advertising to clarify carrier price comparisons following a complaint from T-Mobile challenging the claims made in Sprint’s campaign.

At T-Mobile’s behest, the NAD said it reviewed a number of claims made in the Sprint ads, including statements that customers could “come save 50% on most Verizon, AT&T or T-Mobile rates,” and “cutting your rate plan by 50 percent is easy.” The NAD also looked at Sprint’s disclosure practices for its $36 activation fee in the campaign.

T-Mobile in particular took issue with Sprint’s implied claims that its 50 percent off deal applied to any T-Mobile plan when it was only relevant to T-Mobile’s 2 GB 6 GB and 10 GB Simple Choice Plans.

Sprint argued the distinction was made clear in the fine print of the ads, but the NAD said that wasn’t enough.

“NAD determined that references to the limitations are blurred by the fast-moving audio and visual elements of the commercials which also make the supers, which refer to rate plans as well as limitations and restrictions, difficult to read, notice and understand,” the NAD wrote in its ruling. “NAD determined that the overriding message – that you can have the same rate plan for half the price simply by switching to Sprint – was not supported by the evidence in the record and recommended that the commercials be discontinued.”

The NAD said Sprint permanently discontinued its “Cut Your Bill in Half” ads during the division’s review.

Though T-Mobile told CNET it “called Sprint out on their total BS promises” and was pleased with the result, the Un-carrier has faced criticism of its own marketing practices in the past.

In December, a coalition of consumer groups filed a complaint with the Consumer Financial Protection Bureau (CFPB) accusing T-Mobile of “misleading advertisements and abusive debt collection practices.”

Change to Win alleged T-Mobile has engaged in deception by billing its services as “no contract” obligations though many month-to-month services are tied to two-year equipment financing plans that carry financial penalties for early termination.

Last week, Change to Win took its concerns to the FCC in a letter asking Chairman Tom Wheeler to investigate T-Mobile’s advertising and business practices.

In particular, the group urged Wheeler to review the fairness of T-Mobile’s “no contract” claims as they relate to equipment installment plans; T-Mobile’s offer to pay off early termination fees; and its “pattern of fraudulently enrolling customers in services without their consent or knowledge.”