The Screen Actors Guild has rejected the "last, best and final offer" from major Hollywood studios following negotiations over actors' pay.
SAG members, who have been without a film and television contract since their old deal expired in June, have described the proposed new contract as "regressive and damaging".
The Alliance Of Motion Picture And Television Producers, which represents the studios, had wanted the new contract to start from the date that it was signed and last for three years, while union members wanted it backdated to June and valid for only two years.
In a statement, SAG said: "What management presented as a compromise is, in fact, an attempt to separate [us] from other industry unions. By attempting to extend our contract expiration one year beyond the other entertainment unions, the AMPTP intends to de-leverage our bargaining position from this point forward."
However, the AMPTP defended its offer as "fair and strong", adding: "We simply cannot offer... a better deal than the rest of the industry achieved under far better economic conditions than those now confronting our industry."
SAG has revealed that 73% of its National Board Of Directors rejected the offer, sparking fears of an actors' strike which could have similar consequences to 2007's writers' strike.