LOS ANGELES — The threat of a Hollywood strike is getting real.

On Wednesday, television and movie writers — roughly 12,000, all members of the Writers Guild of America — will begin voting on whether to authorize a walkout. The online vote will end on Monday. If members approve a strike, as they almost certainly will, and no pact with studios has been reached by May 1, fingers will stop typing and picketing will begin the next day.

A strike would have serious implications. When writers walked out a decade ago, the impasse cost the Los Angeles economy an estimated $2.5 billion. As production halted, income dried up not only for writers but also for set decorators, caterers, limo drivers and florists. Fans were not thrilled, either, as television schedules became a sea of reruns.

Here is what you need to know this time around.

How likely is a strike?

Longtime Hollywood power players — agents, studio executives, labor lawyers — put the chance at roughly 51 percent. But it changes by the day.

Tempers have cooled (a bit) over the past week, as negotiators for the Writers Guild and an organization that represents studios, the Alliance of Motion Picture and Television Producers, have made progress on pay increases. But at least one radioactive issue remains unsettled: health care.

And the union could be easily thrown into a rage by a single bit of news. Members were incensed on April 7, for instance, when CBS revealed in a regulatory filing that its chief executive and chairman, Leslie Moonves, had received a 2016 pay package worth $69.6 million, a 22 percent increase over the previous year, when the company did not perform as well.

How would it affect television?

Late-night comedy shows would instantly revert to reruns. Summer reality shows, such as “Big Brother,” would arrive — the writer-producers who work on them have a different contract — but some scripted series scheduled for the fall would most likely be delayed. A strike could be a death knell for daytime soap operas, which rely on a new episode almost every weekday, unless producers bring in nonunion writers, which happened during the last strike.

But there could also be bigger consequences. Most networks have been losing viewers as Netflix and Amazon have risen in popularity. A strike could speed that shift: Streaming services have some big shows ready to go — new seasons of “Orange Is the New Black” and “Stranger Things” on Netflix, for instance — and a huge array of on-demand older programming.

ABC, NBC, CBS and NBC are also set to unveil their offerings for the coming season at mid-May “upfront” presentations in New York. How do you woo advertisers amid pickets? As analysts at Barclays wrote in a report last week, “Given the anemic growth rates for television advertising already, any uncertainty over the fall season is likely to force more advertisers to expand their allocations towards digital platforms.”

What about movies?

At first, it would be business as usual. Because big-budget event films take years to make, summer movies would continue to arrive on schedule. Films with finished scripts — and perhaps some with not-so-finished ones — would continue to go into production. Movie executives really started to sweat the last writers’ strike, which took place in the winter, only when it threatened to derail the Academy Awards, a crucial marketing platform.

How long could a strike go on?

Anybody’s guess. The Writers Guild walked out for 100 days in 2007-8 and 155 days in 1998. In both cases, the most in-demand writers eventually got tired of losing income and applied pressure to wrap it up. (Thousands of guild members are unemployed in any given year.)

Why are writers upset? With the boom in scripted television shows, isn’t there more work than ever?

There are definitely more union-made series — at least 300 last season, or about 40 percent more than two years before that. But networks are ordering fewer episodes per season (10 to 13) than in the past (22 to 24). So a series writing job pays less.

At the same time, in a contract provision known as exclusivity, most TV writers can write for only one series at a time, taking them off the market for up to a year. And to top it off, reruns don’t attract very many viewers anymore, limiting residual payments.

Movie writers say they are hurting because the major studios are making fewer films. Studios have also cut way back on what is development, or the polishing and reworking of scripts to find a good one.

What does the union want?

Negotiators started with a laundry list of requests, including easing that exclusivity rule, but it boils down to raises and bigger payments from studios for the guild’s health plan.

Raises were relatively easy: The Directors Guild of America agreed to a new three-year contract with studios in January, and writers are likely to receive similar wage increases. But the health plan is a bear. In part because it provides extremely generous benefits, the plan has begun to run steep deficits. The union wants the studios to shore it up.

Why won’t studios give it to them?

Movie and TV companies are facing an uncertain future. Consumers are downgrading cable television packages or forgoing a connection altogether. Ad-skipping devices have put pressure on advertising sales. DVD money continues to evaporate. Attendance at movie theaters is flat.

Studios are also adamant that writers agree to fundamental changes in how the union health plan functions to avoid future bailout demands.

Why is it always the writers who are going on strike?

As a rule, the directors are well paid and feel valued by entertainment companies, and the actors’ union can be a bag of infighting cats. That leaves the writers.

According to historians, the friction between “scribes” and studios dates to the end of the silent film era. Studios suddenly needed writers to provide witty dialogue, so they imported wordsmiths from New York. But they treated writers — or at least many writers have felt this way ever since — as expendable stenographers.

Put another way, writers see their craft as artistic expression. For the most part, studios see it as commerce.