Equity, the actors' union, is campaigning for television companies to use professional actors for walk-on parts rather than "cutting corners" with untrained staff.
The organisation claims those not included in its register of 3,000 "background artists" may not know how to behave on set.
The BBC has already signed up to Equity's cause and written to casting agents who supply the extras. "Only if sufficient numbers of professional artists are not available should the question of using non-professional artists arise," the BBC said.
Though Equity can see the funny side, a spokesman said there was a serious point to the campaign. "There is a substantial degree of skill in doing this. People need to know how to behave properly on the set," he said. "It would be disastrous if you had members of the public looking at the actors and collecting autographs and waving at mum. But, of course, some companies try to cut corners."
Entertainment insiders said it was a tricky issue. "The question is whether there is any talent to being a walk-on," said one. "Most proper actors think walk-ons are a waste of space."
And it is privately accepted that when filming is taking place in parts of the country with only a handful of Equity members on the register, the rules may have to be relaxed.
Yet for a small band of people, regular walk-on work is their major source of income – even if at a rate of £80 a day.
The most regular of all, such as those in the television soaps, even acquire a certain cachet. A spokeswoman for EastEnders said several of their best-known walk-ons received fan mail and, in rare cases, said the odd line.
Michael Leader, who plays a character known as the milkman, spoke for the first time in the programme this year after 17 years, nearly the entire life of the show.
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