Royal Mail has been attacked for handing a bigger salary to its new, less-experienced male chief executive than was paid to his female predecessor Moya Greene.
Rico Back, a German who runs Royal Mail's European parcel delivery arm, will get £100,000 a year more than was handed to Greene, one of the most highly regarded chief executives in Britain.
Greene, who has been in charge of the historic firm since 2010, has led it through the biggest-ever public share offer in the UK, and is a skilful negotiator with unions and politicians.
One of her final accomplishments was to fend off strikes by postmen over changes to the company pension scheme.
The 63-year-old stunned the markets by announcing her resignation from Royal Mail yesterday.
The firm swiftly unveiled Back as her replacement. The father of four, who lives in Switzerland, runs Royal Mail's European subsidiary GLS.
However, while Greenewas handed a £548,000 base salary last year, it was revealed Back would get £640,000 – nearly £100,000 more.
The payment sparked outrage from campaigners. It followed a similar situation at budget airline EasyJet, which last November appointed Johan Lundgren, who had never run a FTSE 100 company before, as chief executive on a bigger salary than his predecessor Dame Carolyn McCall.
EasyJet eventually made a U-turn and Lundgren now gets £704,000, the same as McCall.
Sam Smethers, chief executive of the Fawcett Society gender equality campaign charity, said: 'Gender pay gap data shows we repeatedly see women undervalued in the workplace, with the bonus gap even wider.
The difference in salary is huge and appears hard to justify.
'I think Royal Mail has to avoid regarding their women as second-class while the men get first-class treatment.'
The appointment of Back, 63, was a double blow for equality campaigners as it means that there will be just five female FTSE 100 chief executives, from seven at the start of this week. Anne Stevens, boss of engineering giant GKN, left this week.
Greene said low representation of women worried her. She said: 'I know in the UK there is this huge pool of unbelievably talented female executives and I think the UK has got a way to go before opportunity is fairly given to this incredible group.'
Greene, a Canadian who is married to a leading surgeon and has a daughter, is one of the most revered bosses in Britain.
She is credited with transforming Royal Mail into a modern business and leading it through its complex stock market float in 2014. The company employs 142,000 people and delivers to 30m addresses.
Its shares have outperformed the FTSE 100, and since November are up more than 45 per cent.
Despite that Greene is one of the poorest-paid bosses on the FTSE, earning £1.8million last year.
But her corporate skills have seen her appointed to the boards of EasyJet, Rio Tinto and the Tate.
Back, meanwhile, has spent most of his career reporting to Greene as head of the firm's giant European parcels arm. A leading analyst yesterday told of his fear over Back's lack of expertise.
Gender pay has become toxic for FTSE 100 firms keen to say they are equal opportunity employers.
Last night, Royal Mail defended Back's pay. It said it had a median gender pay gap of 1.5 per cent in favour of men, compared to 9.7 per cent among all other firms.
It said that he was only entitled to 17.5 per cent of his salary as a pension contribution – around £112,000 – compared to the £200,000 Greene received.
A spokesman added: 'We have sought to ensure that Moya and Rico's fixed pay and benefits will be the same.'
It said Back is the longest-serving senior executive at Royal Mail and has a deep understanding of the business.