The Liberal Democrats said it will leave a “bitter taste” if she claims the payment after he brief and tumultuous tenure in Downing Street.
The public costs duty allowance was introduced in 1991 to support former prime ministers in their public duties after they leave office.
Lib Dem cabinet office spokeswoman Christine Jardine said: “Liz Truss is facing calls to turn down the allowance of up to £115,000 a year she will be entitled to as a former prime minister.
“There is no way that she should be permitted to access the same £115,000-a-year for life fund as her recent predecessors – all of whom served for well over two years,” she said.
“For Truss to walk off into the sunset with a potential six figure dividend, while leaving the British public to suffer, would be unconscionable.”