The moves come after co-stars Mayim Bialik and Melissa Rauch recently inked new deals with studio Warner Bros, the Hollywood Reporter said.
Emmy winner Parsons (Sheldon), Galecki (Leonard) and Cuoco (Penny) will negotiate together, as they did in 2010, and are looking for a considerable bump in pay from their current deal.
The trio currently earns USD 325,000 per episode and may seek up to USD 1 million an episode.
Original stars Simon Helberg (Howard) and Kunal Nayyar (Raj) also are said to be looking for increases and will renegotiate together.
CBS has renewed 'The Big Bang Theory' through its upcoming seventh season, which begins next week.
The series is up for the best comedy Emmy this year, with Parsons again in the running for best actor. The show has yet to win in the comedy series category.
