The famed artist sold the huge bronze artwork, named Draped Seated Woman, to London's Tower Hamlets council in 1960, and insisted that it was displayed in a poor area of the U.K. capital.
However, after it was vandalised during its stint in Stepney, East London, the work was moved to Yorkshire, England in 1997.
Now Tower Hamlets' mayor Lutfur Rahman has announced officials are planning to sell the piece, which is estimated to be worth $36 million (£20 million), to boost the council's capital during a time of economic struggle in Britain.
The move has angered Moore fans, and Slumdog Millionaire filmmaker Boyle has now thrown his support behind a bid to stop the sale by adding his name to an open letter from a string of protesters, including Moore's daughter, Mary.
The missive, published in Britain's Observer newspaper, reads, "While we understand the financial pressures that Tower Hamlets faces, we feel that the mayor's proposal goes against the spirit of Henry Moore's original sale to London County Council at a favourable price on the understanding that it would be placed in East London.
"The presence of the sculpture in Stepney was a demonstration of the postwar belief that everyone, whatever their background, should have access to works of art of the highest quality... We hope that Tower Hamlets will reconsider and find a suitable location that continues to honour Moore's idealistic vision."