PORTLAND – A weak advertising market was blamed for the layoffs of 20 workers at Resort Sports Network, a Portland-based company that provides outdoor-information spots for the cable TV industry.

The company said Monday that the layoffs amounted to 15 percent of its nationwide work force of 132.

Advertising weakness was cited in several areas, including RSN’s resort television network, its outdoor updates on several cable TV channels and its Web site.

“We are not immune to the advertising downturn in the national marketplace. Our downsizing is a direct response to the same forces that are affecting media companies throughout the country,” said Bill Burke, RSN’s president and chief operating officer.