Iran Press/ Europe: At least £87 million has been pledged in aid to the Middle Eastern country, down from £164m in 2019-2020.
A Foreign Office spokesman said the government remained "steadfast" in its support to the Yemeni people.
Yemen is among several Middle Eastern and African countries whose UK aid is at risk, a leaked email suggests.
First reported by open Democracy, a leaked document dated last month suggests officials are considering cutting aid to Syria by 67% and Lebanon by 88%.
Aid to Nigeria could drop 58%, Somalia 60%, South Sudan 59%, and the Democratic Republic of Congo by 60%, it says.
In a letter to Boris Johnson, charities say the government has made a "misjudgment" by thinking the public is happy to turn away from countries affected by poverty, war, and disease.
"History will not judge this nation kindly if the government chooses to step away from the people in Yemen and thus destroy the UK's global reputation as a country that steps up to help those most in need," the letter says.
Oxfam, Christian Aid, Save the Children and Care International are among the 101 signatories.
Danny Sriskandarajah, Oxfam GB chief executive, said: "Aid cuts are a false economy that will remove a vital lifeline from millions of people in Yemen and beyond who can't feed their families, have lost their homes, and whose lives are threatened by conflict and Covid."
He also urged the government to stop the "immoral" practice of selling arms to the war-torn state.
MPs from across the political spectrum have criticized the reduction in aid.
Conservative former international development secretary Andrew Mitchell said the "unimaginable" move would "condemn hundreds of thousands of children to starvation".
Shadow foreign secretary Lisa Nandy said the change represented the UK "abandoning our moral obligations".
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