The creator, 49, and colleagues Brian Boyle, Matt Weitzman, Rich Appel and Alec Sulkin have walked out in a show of support to the writer’s strike.
MacFarlane voices Peter Griffin in the animated cartoon and won’t return until the strike is over, according to sources.
An insider told Deadline: “There is quite a bit of runway to go before the wheels come off. The animated satire has about three months of scripts, v/o, etc already completed. Then the studio will have to figure out what steps to take next.”
Family Guy ended its 20-episode 21st season last week on May 7.
MacFarlane also works on American Dad, which started its 20th series in March.
The Standard has contacted Mr MacFarlane’s publicist for comment.
Thousands of film and TV writers have hit the picket lines after the Writers Guild of America called its first strike in 16 years.
America’s most popular late-night comedy shows were shut down and aired re-runs last week, and the strike is now hitting planned TV shows and movies.
The last strike lasted 100 days, beginning in 2007 and ending in 2008, and Seth joined strikers when this happened.
An estimated 11,500 members have been on strike since midnight on May 2 after talks with the Alliance of Motion Picture and Television Producers over pay fell apart.
The dispute is primatily over the rise of streaming - with the guild claiming that even as budgets have increased, writers’ share of that cash has consistently shrunk.
Game of Thrones writer George R.R. Martin announced that the writer’s room on spin-off series A Knight of the Seven Kingdoms: The Hedge Knight would halting for now.
The creator of the Game of Thrones universe pledged his full support for the strikers, writing on his blog: ‘I am not in LA, so I cannot walk a picket line as I did in 1988, but I want to go on the record with my full and complete and unequivocal support of my Guild.’
‘There are pickets in front of every studio lot and sound stage in LA, and many in other cities as well. Get used to them. I expect they will be there for a long time,’ he said.
He added that filming would continue on the Game of Thrones prequel House of the Dragon, which started in the UK on April 11.
The show is the latest in a growing list of series hit by the walkout.
The creators of Netflix hit Stranger Things confirmed on the weekend that production on season five has been delayed.
Creators Matt and Ross Duffer, both 39, known as the Duffer Brothers wrote on twitter: “Writing does not stop when filming begins. While we’re excited to start production with our amazing cast and crew, it is not possible during this strike.
“We hope a fair deal is reached soon so we can all get back to work. Until then - over and out.”
While the fifth and final season of the sci-fi horror was announced last February, a release date has not been set.