US writers and actors are calling for a code of conduct to govern product placement in TV shows and films.
Eva Longoria's character promoted cars in Desperate Housewives
Unions said the growing practice of including products for money or other services amounts to hidden advertising.
The Writers Guild of America and the Screen Actors Guild want any deals with outside firms to be disclosed at the start of transmission.
The campaign comes as products are increasingly woven into storylines and reality TV shows.
But advertising industry watchers predict the trend of in-programme promotions could be set to rise further on TV as personal video recorders allow viewers to cut out commercials.
Product placement has been evident in films for many years.
Reality TV shows such as The Apprentice have recently featured episodes where contestants work with sponsors.
And an episode of Desperate Housewives saw Eva Longoria's character Gabrielle take on a modelling job in which she promoted car manufacturer Buick.
The unions said they may appeal to regulators if studios do not take action.
They want viewers to be told if they will be "subject to hidden or stealth advertising".
According to the Writers Guild, its members are being told to include "lines that sell this merchandise and to deftly disguise the sale as a story".
The proposed code would require the studios to give actors, writers and directors a say in how products are featured.
"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.
Product placement is currently outlawed on TV in the UK but regulator Ofcom has announced it was looking at the issue with a view to consulting broadcasters about a possible rule change.