The last hurdle to Warner Bros. TV and CBS clinching a two-season renewal of “The Big Bang Theory” is setting a new contract with actresses Mayim Bialik and Melissa Rauch.

According to multiple sources, the five original cast members on the show – Jim Parsons, Johnny Galecki, Kaley Cuoco, Kunal Nayyar and Simon Helberg — made the extraordinary gesture of taking a small pay cut to free up money for raises for Bialik and Rauch. The move is evidence of the strong camaraderie among the key players on the show that remains primetime’s most-watched comedy. The general harmony behind the scenes has also contributed to the show’s enduring creative strength, bolstered by the comedic chops of the core ensemble.

But as the dealmaking for what might be the final two seasons of “Big Bang” hits the home stretch, reps for Bialik and Rauch are said to be pressing for the studio to add some more coin to their paychecks as well.

Bialik and Rauch both joined “Big Bang” in season three and thus have to date earned significantly less than their co-stars. Both actresses are in the $200,000 per episode range this season, the show’s 10th, compared to $1 million per episode for the original five.

In the renewal talks that began late last year, the original cast members agreed to take a $100,000 cut in salary for the prospective 11th and 12th seasons to free up $500,000 to fund raises for Bialik and Rauch.

If Bialik and Rauch split the $500,000 from their co-stars, both would rise to nearly $450,000 an episode, or more than $21 million for the two-year, 48-episode deal. The question now is whether the two will hold firm for parity, or at least closer to parity, with the other stars. Negotiations on Bialik and Rauch’s deals are just beginning in earnest this week.

There’s little debate about whether the actresses have become integral to the world of “Big Bang.” Bialik’s Amy Farrah Fowler is the girlfriend of Parsons’ Sheldon Cooper, a relationship that has added emotional depth to the show. Rauch’s Bernadette Rostenkowski had a baby earlier this season with Helberg’s Howard Wolowitz’s character, which provided another source of highly rated episodes. Bialik has nabbed four consecutive supporting actress Emmy noms from 2012-15.

In the last “Big Bang” contract renewal cycle, Helberg and Nayyar secured raises that eventually brought them to seven-figure parity (as of this current season) with Parsons, Galecki and Cuoco.

But the timing for Bialik and Rauch to reach the high six-figure threshold is not as optimum as it was three years ago for Helberg and Nayyar.

The show has grossed over $1 billion in syndication for Warner Bros. Because of the way the cable and broadcast syndication deals are structured for long-running shows, “Big Bang” won’t generate much incremental revenue from the additional 48 episodes to come in an 11th and 12th seasons.

Cabler TBS and the TV stations that carry “Big Bang” reruns pay for the show by the week, not by the episode, for a pre-set license term. That means Warner Bros. will make the same fees with the existing 230 episodes as it would by adding another 48 installments to the mix. An SVOD licensing deal for “Big Bang” is believed to be in the works at long last (now that cable and broadcast syndication exclusivity terms have ended) but that too will most likely be based on a flat fee for a license term rather than an episode-based pricing model. With the big SVOD outlets increasingly plowing more resources into original programming, spending on off-network acquisitions has become tighter. “Big Bang” will surely draw strong interest, but the promise of additional episodes to come in 2018 and 2019 probably won’t drive the pricetag higher.

And finally, CBS’ license fee for the show no longer covers all production costs, as it did in earlier seasons. That fee is believed to be in the $6 million-$7 million range under the new deal. The salaries of the five original actors alone take up $5 million of that fee.

As a business proposition, the “Big Bang” cast renewal deals also come as Warner Bros. TV parent Time Warner is in the midst of navigating its $85.4 billion merger agreement with AT&T. In this environment, spending decisions are being heavily scrutinized. As successful as “Big Bang” has been for the studio, the new episodes won’t yield the kind of windfall for the studio that might otherwise grease the wheels for dealmaking in the coming days for Bialik and Rauch.

There is optimism at both the studio and the network that a deal will get done.

Reps for Warner Bros. TV, CBS, Bialik and Rauch declined to comment.