A dispute between Hollywood studios and screenwriters could lead to the first writers strike in a decade.
The current deal expires at midnight Pacific Standard Time (08:00 BST). Formal talks to reach a new deal have been going on since 13 March.
Officially the two sides are not commenting on negotiations, but reports suggest a compromise is in the works.
The Writers Guild of America (WGA) wants higher pay per episode and royalties for reruns.
The writers' union, which represents about 9,000 people, says its members have been squeezed, as studios commission shows with fewer episodes, but lock up writers with exclusive contracts.
The union also says writers are not sharing enough of the profits made from online streaming, which keeps shows and movies alive for years after first airing.
The union estimates the average salary for TV writer-producers fell 23% in the last two years.
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It says its requests would add about $156m in costs for the major production companies, which include firms such as 21st Century Fox and Time Warner.
"The undeniable truth is that these costs are very affordable for these profitable companies," it said in a post on its website.
About 96% of more than 6,000 WGA members voted to strike last week. Some took to social media to express solidarity, changing pictures on Twitter to spotlight their support.
A strike would first affect topical shows, such as Saturday Night Live, which have enjoyed higher ratings since the election of Donald Trump as President, who has proved an popular target for news satire.
The impact would be felt more slowly elsewhere.
But analysts said the threat posed by online services, such as Amazon and Netflix, puts pressure on major broadcasters and cable companies to avoid a work stoppage.
The Alliance of Motion Picture and Television Producers, which represents conglomerates such as Comcast Corp, Walt Disney Co and CBS Corp, said last week it is "committed to reaching a deal ... that keeps the industry working."
Stephen Burke, a Comcast executive, told investors last week he was "optimistic" that the issues would be resolved.
"Strikes aren't good for anybody," he said. "The people on both sides of the table tend to lose and I'm hopeful that we're going to get it done."Image copyright Angela Weiss/Getty Image caption Writer Billy Ray, right, has worked on films such as The Hunger Games is one of the people leading negotiations for the Writers Guild of America
The last WGA strike - a 100-day stoppage in 2007-2008 - cost the Californian economy an estimated $2.1 billion in lost output, according to a Milken Institute review.
TV viewership dropped 21% in the first week, according to Nielsen figures.
Online television was in its infancy at the time. Today, Amazon and Netflix are major competitors for eyeballs and have a deep reserve of programs to buffer them from viewer demands for new content.
Those companies are not exempt from union demands.
But they would be likely to emerge as big winners in any prolonged strike, which could lead to "lasting changes in viewership patterns", Barclays Capital analyst Kannan Venkateshwar wrote in a research note.
Theodore Sarandos, the chief content officer at Netflix, told investors last month that the firm was "keeping an eye" on the situation and some productions could be held up by a strike.
"Our fingers are crossed that, that won't happen," he said.