LONDON — The Man Booker Prize is Britain’s most prestigious literary award. But for the past two years, American writers have dominated the competition — and authors from Britain and the Commonwealth countries are none too pleased.

The crescendo of frustration may have reached a peak. A group that counts the literary heavyweights Margaret Atwood, Ian McEwan and Zadie Smith among its members has fired a shot across the bow, demanding that the Man Booker Foundation reverse a 2014 decision making any novel written in English and published in Britain eligible for the prize.

Leading authors and critics from the group, the Rathbones Folio Academy, bashed the Booker’s policy anew this week, arguing that changing the rules had taken away the distinctiveness of the prize, which was previously limited to writers from Britain, Ireland, Zimbabwe and the Commonwealth.

They also criticized the way in which the Man Booker, begun in 1969, had highlighted less well known and prominent literature.