Los Angeles ? Hollywood writers and actors are calling for a code of conduct to govern a growing trend of hidden advertising in TV shows and films, and they say they will appeal to federal regulators if studios don’t respond.

The also want their share of the billions of dollars in advertising revenue generated by what they write and act in, their unions say.

Advertising has been creeping into programming for years, blurring the lines of ads and entertainment. It can be as simple as a Coca-Cola cup prominently displayed on “American Idol.”

But increasingly, the products are becoming integrated into story lines as well.

The character Gabrielle on “Desperate Housewives” was seen last season as an auto show model touting Buick. Some reality shows base entire episodes on contestants working with sponsors. Contestants on “The Apprentice,” for example, have been given tasks involving Burger King, Home Depot and the DVD release of the latest “Star Wars” film, among others.

The Writers Guild of America released a study Monday calling for a code of conduct that would mandate full disclosure of all product integration deals at the beginning of a program so viewers would know they will be “subject to hidden or stealth advertising,” according to a news release.

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“Just as there is an established right to truth-in-advertising, there should be a similar right to truth-in-programming where advertising is concerned,” said Screen Actors Guild President Alan Rosenberg.

The code also would require the issue to be discussed in bargaining with the studios to give actors, writers and directors a voice in how products are woven into the plot.

“We are being told to write the lines that sell this merchandise and to deftly disguise the sale as a story,” the study states.

The effort is part of a larger push by the WGA to unionize writers, producers and editors who work on reality TV shows.

The guild has said many of the “unscripted” shows are actually carefully crafted by editors who often write specific dialogue or piece together bits of video to tell a story.

A representative of the Alliance of Motion Picture and Television Producers, which represents film and TV studios, did not immediately return a phone call seeking comment Sunday.

Nick Counter, the AMPTP’s president, has called the WGA’s aggressive stance on the issue “an unfortunate tactic” in the past.