In an internal letter this week, WGA leaders told members who have volunteered to serve as strike captains to be prepared for immediate action should a work stoppage be triggered after the guild’s contract with producers expires at midnight PT out May 1.

“If it happens, we will be out there on May 2 with signs,” a union insider told Variety.

That dispels any notion that the writers would delay picketing at the start of a strike, a move that had been considered. It also raises the possibility that media buyers and others will have to pass picket lines on their way into the major networks’ upfront presentations in New York.

Contract talks between the guild and the Alliance of Motion Picture and Television Producers resumed on Tuesday after a weeklong break. The clock is ticking for negotiators as the contract expires in five days. Sources close to the situation said there were lengthy discussions at the bargaining table on Tuesday but not much in the way of progress.

Given the timing, the first major events coming up on the industry calendar in May are the broadcast upfronts and the Cannes film festival, which runs May 17-28.

The upfronts begin their usual marathon week of presentations for the largest networks on May 15, with NBCUniversal’s combined cable and broadcast show kicking off the presentations and Fox making its case later in that afternoon. Univision, ABC, ESPN, CBS, Turner, and the CW will also make their pitches to advertisers in the ensuing three days. But the current dispute between the WGA and producers threatens to cast a pall over a week when television executives strain to project a relentlessly upbeat tone.

Conversations about how a strike would impact the fall season are in full effect inside network and studio offices, sources tell Variety. The consensus is that a short strike that only lasts a few weeks in May or into early June would not be problematic for production of the new fall season. But a strike that extends into July or August — or one that is delayed until then through short-term contract extensions — could have radical effects on production, forcing the networks to lean heavily into unscripted programming, push back fall premieres, and shorten season orders.

Whether or not that worst-case scenario comes to pass, the potential for it will loom large over upfronts. Unless writers and producers come to an agreement quickly, networks will be forced to acknowledge the labor dispute at their presentations.

“We’ll have to talk about how we don’t know what the future will hold,” one network insider told Variety. “But everyone knows that the strike will end. And when the strike ends, the programs you pick are the programs you pick.”

That uncertainty will be on ad buyers’ minds as they cut their deals, but is unlikely to have much impact on the nature of those agreements. Should a strike have an impact on fall programming plans, advertisers will have protections worked into their deals, as they always do, that will allow them to get money back or make-goods.

At the presentations, however, uncertainty will likely mean less emphasis on fall primetime schedules. Showcasing those schedules has long been a core function of the upfronts, but one that networks have de-emphasized as they have moved toward selling ads against C7 ratings, which cover a week’s worth of delayed viewership.