AT&T (T) - Get Report slid Tuesday after an industry analyst, skeptical of the telecom giant's ability to hit its 2020 revenue target, issued a rare sell recommendation on the shares.

AT&T's stock at last check fell 4.61% to $37.81 after MoffettNathanson downgraded the Dallas company's shares to sell from neutral.

The move became just the second sell rating from the more than 30 analysts currently covering the stock, according to Bloomberg.

AT&T's forecast for 2020, including 1% growth, "doesn't sound challenging," wrote analyst Craig Moffett, but "the more we poke at our estimates, the harder it is for us to imagine they can be achieved."

Moffett did affirm his $25-a-share price target on AT&T.

In particular, Moffett sees declining growth, in the mid-single digit range, across 60% of AT&T's business lines, including a declining number of subscribers and falling video revenue at its entertainment group.

As it prepares to launch its HBO Max streaming service in the spring, AT&T is also grappling with a fall in ratings at Warner Media, the MoffettNathanson analyst wrote.

That leaves AT&T's wireless business to try and pick up the slack, a task Moffett argues is challenging given the fierce competition in the sector.

HSBC also recently issued a research note warning of tougher times ahead for the telecom industry as well, with AT&T one of the companies on the list.

Rival Verizon (VZ) - Get Report recently reduced prices for its unlimited plan, while AT&T's new offerings are "a bit aggressive," wrote HSBC analyst Sunil Rajgopal.

The HSBC analyst also cast doubt on the economics of AT&T's HBO Max streaming service, nothing the high costs shouldered by other players in the industry.