Monthly bills for Comcast Corp. Xfinity customers in the Philadelphia area and South Jersey will go up about 4 percent on Jan. 1, with higher prices for cable TV and Internet services plus elevated fees.

The Philadelphia-based company began informing customers of the changes online on Friday and in mailings with bills this month.

Comcast isn't raising prices across the board, but is boosting them at varying levels on different cable packages or Internet services, according to the new rate card. The prices on some products declined.

For the first time, it appears that competition from online streamers is having an effect on Comcast's premium channel prices.

Comcast slashed the cost of HBO by 32 percent, to $15 a month from $21.95, matching the HBO Now streaming service from Time Warner. Time Warner launched the stand-alone HBO Now this year, leading some to think that pay-TV subscribers interested in Game of Thrones and other HBO entertainment could cut the cord and watch the streamed channel. Comcast also cut prices on Showtime, Starz, Cinemax, and the Movie Channel.

Consumer advocates say that cable bill inflation has outpaced general inflation for many years, and that Comcast and other pay-TV operators force subscribers to buy programming they don't watch through channel bundles.

Hannah Sassaman, policy director for the nonprofit advocacy group Media Mobilizing Project, said the higher Comcast prices come after many people in Philadelphia complained this year about the cost of TV and Internet services during Comcast's negotiations for a 15-year franchise renewal with the city. A new franchise agreement has not been finalized.

Comcast spokesman Jeff Alexander said the company continues to invest in its network and technology "and to give customers more for their money - like faster Internet service and more WiFi hot spots, more video across viewing screens, better technology like X1, and a better customer experience."

Comcast said the national price boost for subscriber bills on a "weighted average" will be 3.9 percent, and Philadelphia-area and New Jersey residents can expect the same.

Digital adapters for additional televisions in homes to access cable channels will rise to $3.99 a month from $2.99 a month, a 33 percent boost.

Many Comcast Xfinity customers have two or three TVs in their homes - which could result in an additional $1 or $2 a month. Nationally, a price hike on digital adapters will generate an additional tens of millions of dollars in revenue for Comcast.

Comcast also will hike a "broadcast TV fee" by 66 percent to $5 a month from $3. This relatively new fee covers the cost of retransmission fees that over-the-air broadcast TV networks - CBS, NBC, ABC, and Fox - charge cable companies for distributing their networks on pay-TV systems.

Retransmission fees and sports are the two biggest inflationary-costs pressures in TV bills, according to industry observers and Comcast executives.

"Digital starter" - an entry-level package - remains unchanged at $69.95 a month. "Digital preferred plus two premiums" fell 6.7 percent to $111.90 a month from $119.90.

Meanwhile, triple-play bundles - TV, Internet, and phone services - were generally hiked by $2.50 a month, and several double-play bundles - only TV and Internet services - were boosted $3 or $4 a month.

The prices on the "expanded basic" tier of service were relatively unchanged as were prices for international channels and telephone services.

bfernandez@phillynews.com

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@bobfernandez1