The annual series of glitzy presentations, held in May in New York City by major television broadcasters, is one of the most important advertising sales periods, with nearly half of an advertiser's video budget allocated for the next television season.

The backdrop of this year's presentations was different. Ad buyers were greeted by picket lines outside Radio City Music Hall on Monday, celebrities like Pete Davidson and Edie Falco, who attended last year's NBCU presentation, were replaced by news personalities like "Squawk Box's" Andrew Ross Sorkin.

An estimated $18.79 billion in ad spending could be committed for the upcoming season, up a modest 0.8% from the current season, according to researcher Insider Intelligence.

This year, advertisers and ad agencies may well use the strike as a bargaining tool, said Erin Firneno, vice president of business intelligence for researcher Advertiser Perceptions.

"While it won't necessarily cause them to allocate fewer dollars upfront, it will help buyers get more flexibility in their contracts, something buyers have been pushing for," said Firneno.

The writers' strike, which has entered its third week, is also injecting a new element of uncertainty for ad buyers, at a time when television viewership is declining and the possibility of recession looms. The walkout that began May 2 caused most late-night shows to go dark and halted or delayed production on such high-profile series as Netflix's "Stranger Things" and HBO's "Hacks."

A protracted dispute may jeopardize the programming lineup for the fall season. And contracts with two other major Hollywood unions, the Directors Guild of America and the Screen Actors Guild-American Federation of Television and Radio Artists, expire on June 30.

While the TV networks have long contended with splintered viewership amid the rise of social media and streaming, the writers' strike puts content production at risk, said Rishad Tobaccowala, a former executive at advertising and public relations giant Publicis Groupe and advisor on business transformation.

"Marketers just want to sell stuff and build brands," he said. "TV networks are becoming less and less of a driver for that."

In his opening remarks Mark Lazarus, the head of Comcast Corp's NBCUniversal Television and Streaming, acknowledged the picketers.

"We are grateful for the contribution writers made to our company and respect their right to demonstrate," Lazarus said, acknowledging a resolution may take time.

Last year, NBC's upfront presentation emphasized star power as the network returned to a live event after a COVID-19-imposed hiatus. The all-star lineup included a performance by Kelly Clarkson and appearances by Jimmy Fallon and Mariska Hargitay, among others.

Because of the strike, NBCU's presentation this year relied more heavily on its news talent including "Today" show co-hosts Savannah Guthrie and Hoda Kotb; as well as musical performances by Nick Jonas and Reba McEntire.

Ahead of the upfront presentations, media executives sought to reassure investors about the strike's impact. On May 9 Fox Corp Chief Executive Lachlan Murdoch said that the timing of the strike created some "hesitancy," adding that Fox is well-positioned because it focuses on two areas not likely to be impacted - news and sports.

Paramount Global Chief Executive Bob Bakish told investors on May 4: "We've been planning for this. We do have many levers to pull. And that will allow us to manage through the strike even if it's for an extended duration."

(Reporting by Dawn Chmielewski in Los Angeles, Helen Coster in New York and Sheila Dang in Dallas; Editing by Anna Driver)

By Dawn Chmielewski, Helen Coster and Sheila Dang