It is understood the trio - each on salaries in excess of $1 million - walked after 10 refused to up their pay by more than 40 per cent.

The cooking reality show - once the highest-rating program in Australia - will return in 2020, with a panel of new judges yet to be announced.

Last week's Wednesday episode averaged 720,000 city viewers, with just 605,000 on Sunday.

A network spokeswoman said the judges' departure is unrelated to recent coverage of wage underpayment by restaurant empire Made Establishment. Calombaris is one of the directors, and Made Establishment has been under fire over revelations that staff were underpaid a collective total of $7.8 million.

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Recently, a network insider predicted the scandal would limit Calombaris' capacity to negotiate a pay rise.

"It wouldn't be a good look for George to be insisting on more money at this point," the person said.

While the company was fined a "contrition" penalty of $200,000 by the Fair Work Ombudsman, it didn't stop more 20,000 people signing a petition demanding 10 sack Calombaris.

"Channel 10 has made the right decision in [not re-hiring] Calombaris," said Mark Morey, Secretary of Unions NSW. "Hopefully in the future Channel 10 will select MasterChef judges who viewers and contestants can aspire to - chefs who pay their workers fairly. It's a pity Channel 10 hasn't publicly condemned the illegal behaviour."

In addition to their salaries, the judges also enjoy lucrative sponsorship deals related to their participation in MasterChef. Their exit could put these sponsorships at risk.

More broadly, it underscores the pressures facing commercial TV in 2019.

A few decades ago, most broadcasters threw money at their biggest stars. Occasionally, they'd poach one with a huge offer - then send them on "gardening leave", with no on-air role, simply to thwart rival networks.

One 10 insider said MasterChef's production expenses came under scrutiny in 2017, when the network embarked on a cost-cutting mission.

"They were paying huge sums to fly in guest stars like Nigella Lawson - and that's fine, as long as you're getting the ratings and revenue to cover those costs," the source said.

"But when the revenue goes down - and that's a problem faced by every established broadcaster in the world - then tough decisions must be made."

Network CEO Paul Anderson said MasterChef is bigger than its high-profile judges.

"We're obviously disappointed that we couldn't come to an agreement, but that's life," he said.

"The true heroes of the show are the contestants and I don't think we should lose sight of that. [The program] attracts great talent like Curtis Stone and Gordon Ramsay, and I'm sure there's going to be no shortage of people putting their hands up to be part of our new judging panel.

"We've had 11 amazing years of this show, which is far longer than the norm ... we're looking forward to another decade.

"There's no doubt that everyone needs to look after their pennies more in this industry and this will inevitably lead to networks making harder decisions. The days of just throwing money at problems are gone. We're being pragmatic and fiscally responsible but by the same token, we have one of the most successful shows of all time in this country and we need to ... build it for the future.

Anderson said the choice of new judges will be "the million dollar question".

"We have an amazing array of judges that have appeared on the show over the years, from Australian talent like Maggie Beer and Curtis Stone, to [international chefs] like Gordon Ramsay and Nigella Lawson. That process will start in earnest now.

"We've also developed, across the 11 seasons, a lot of home-grown talent.

"We'll be looking at all options. We've had these amazing cooks that have come through the ranks, from Julie Goodwin to Poh Ling Yeow, and that speaks volumes for what this franchise has done not only for cooking in this country, but the talent it's developed."