Local MP Alan Mak has condemned a £691,000 'incentive' payment made to Southern Water chief executive Lawrence Gosden.
The company's annual report shows he has been awarded the money on top of his salary of £687,000.
Mr Mak has now joined other Conservative MPs whose constituencies are served by Southern Water to call on Mr Gosden to voluntarily forego or repay it.
He co-signed a letter to Mr Gosden that said: "As representatives of our constituents, it is our duty to convey to you the strength of public feeling against this morally indefensible award.
"At a time when Southern Water is undergoing intense scrutiny for a plethora of environmental failures across our constituencies, this award is tone-deaf and undermines any remaining thread of public confidence which remained in your company."
Mr Mak said a rise in household costs - including a prospective 46.7% rise in Southern Water bills - made it indefensible for Mr Gosden to receive a 100% pay increase the same year customers are paying more for poorer services.
The letter continued: "The service provided by Southern Water and its extensive record of sewage discharges, infrastructure failures, and water restrictions continues to fall short of the expectations of our constituents.
"The Conservative Party stands for responsible business, fair merit, and accountability. This payout undermines all three, and we expect better from companies entrusted with critical elements of our national infrastructure.
"With this in mind, we urge you to demonstrate leadership by voluntarily foregoing or repaying this incentive. This gesture of good faith would go far in rebuilding credibility with customers and demonstrating your commitment to your turnaround plan."
