Ozzy and Sharon Osbourne starred in their own MTV reality show
US television writers have been warned against working on a new comedy-variety show hosted by the Osbournes.
The Writers Guild of America (WGA) has written to its members telling them they could be subject to a fine if they accept work on the series.
The WGA refuses to work with the show's production company Fremantle over claims that it underpays staff.
In a letter the WGA said: "Any members who perform writing services on that show do so at their own peril."
WGA bosses said they had attempted to negotiate a contract for the Osbournes' show - which has the working title The Osbournes: Live and Dangerous - but Fremantle had declared the talks were at an end.
However, Fremantle said it was the WGA which was responsible for breaking off talks.
It added that the union then "implemented their usual mendacious strategy of feeding misleading and erroneous information to the press".
The WGA said it believed denying the company of writing talent would mean they would see "the wisdom and creative advantages of signing a WGA contract".
In July, the WGA launched a protest against American Idol, claiming the TV talent show underpays workers.
The protest is part of a long-running dispute between the union and producers of many reality TV shows.
The WGA has sought to represent reality show workers since 2005, arguing the work they do is a form of writing.
Many reality TV shows are not covered by WGA contracts, unlike scripted dramas and comedies.