London Mayor Ken Livingstone is considering legal action against plans to close 171 post offices across the city.
The Post Office proposal would see almost a third of branches in areas including Kingston closed, removing services vital to residents, Mr Livingstone said.
"I have taken legal advice on the feasibility of a legal challenge to the announcement that 171 post offices will be closing in London and the Post Office's consultation," Mr Livingstone said.
"The Post Office have said they will consult for just six weeks over the closure proposals rather than the normal 12 weeks which the Government recommends as a minimum.
"London's post offices provide vital support for those who are most in need, particularly the elderly, disabled and those with young children.
"I believe we need more, not fewer, post offices in London. I will be writing to the Post Office informing them of my intention to launch a legal challenge to their decision."
One of the hardest hit areas is Kingston, which has six branches earmarked for closure.
Two post offices in Kingston, two in New Malden, one in Surbiton and one in Worcester Park could be closed as early as July.
It is part of a nationwide cull of 2,500 post office branches. Of the 681 branches in London, 169 have been nominated for closure along with two major centres.
The Post Office says the planned closures are branches that are underused.
It says the cutbacks are needed to make it more competitive.
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