Dish Network Corp. plans to unveil the first major online television service from a cable or satellite company, a $20-a-month set of 12 channels that targets U.S. customers who don't want to pay for larger, more expensive TV packages.

Called Sling TV, the service will offer live feeds of sports, news and scripted shows on TVs, computers and mobile devices. Walt Disney Co.'s ESPN, Time Warner Inc.'s TNT and CNN and others have agreed to supply cable channels.

Pay-TV companies experiencing little or no subscriber growth are being forced to offer products that aren't tied to the traditional TV bundle to compete with cheaper Internet-based services that have attracted customers. Netflix Inc. has more customers than any single cable or satellite operator, with 37 million U.S. subscribers for an on-demand streaming video service that costs $8.99 a month.