The publisher of Sports Illustrated sent layoff notices to most — and possibly all — of its journalists on staff on Friday, the staff's union said.

Authentic Brands Group, the magazine's owner, has terminated its licensing agreement with The Arena Group to publish Sports Illustrated, according to Front Office Sports, which first reported news of the mass layoffs.

"This is another difficult day in what has been a difficult four years for Sports Illustrated under Arena Group (previously The Maven) stewardship," the union said in a statement. "We are calling on ABG to ensure the continued publication of SI and allow it to serve our audience in the way it has for nearly 70 years."

The layoff news comes a day after the publisher announced a "significant reduction" of its 100-staff member workforce, citing "substantial debt" and missed payments.

Authentic Brands Group did not immediately respond to NPR's request for comment.

This is a breaking news story and will be updated.