Meanwhile it is reported that the transport company's "operational deficit" is to reach £1 billion next year, having swollen from £171 million in 2012/13.
The lack of money in TfL's coffers has led to the tube upgrade program on the Northern and Jubilee lines to be scrapped, but departing staff took a total of £51.4 million home last year in severance pay.
The Mayor, who is the chairman of TfL, announced that all senior staff pay at the Greater London Authority will be reviewed following the discovery that TfL has paid more than £50 million in severance each year for the last two years.
The majority of TfL's losses have been blamed on a decline in the number of passengers, while it has also been forced to accept an annual funding cut of £700 million over five years from the government.
As a result, London's transport operator is being forced to go on a major financial diet, cutting operational costs by £608 million in 2017/18. The Mayor attributes the savings to a reduction in "unnecessary management layers".
Transport for London has also decreased the number of staff earning six-figure salaries. In 2017/18 this dropped by 11%, with 169 employees taking home pay packets over.
The reduction in the number of staff in the highest wage bracket will save TfL a crucial £111 million a year by 2020/21.
However in 2017/18 TfL paid 224 people on a base salary of less than £100,000 a one-off six-figure payment, taking into account severance pay.
There were also 71 instances of overtime payments taking employees over the £100,000 threshold.
While Sadiq Khan's review won't be looking to change existing contracts, which include terms for salary in lieu of notice, a one-off voluntary severance payment and payments for annual leave not taken, it will impact future appointments.
Sadiq Khan, Mayor of London, said: “It is essential that London and the GLA continues to attract the very best talent from around the world, and this expertise is essential in keeping London moving and delivering huge projects like the Elizabeth Line opening later this year.
"However, with cuts in funding from central Government across the GLA group, we have to continue to be sharply focused on ensuring taxpayer money is well spent.
“TfL have taken huge strides in cutting their year-on-year operating costs and reducing the number of senior staff is an important part of this.
"We have to abide by pre-existing contractual commitments, but I want to ensure that future contractual arrangements for senior staff are in the best interests of Londoners.”