Mary Cameron who served for years as a magistrate, confirmed to the 'Daily Mirror' that she had signed a petition battling to save children's centres designated for closure by the Conservative-run Oxfordshire County Council.
"My name is on the petition but I don't want to discuss this any further," she said.
The petition, backed by the campaign group 38 Degrees and signed by about 10,000 people, says: "Our children's centres are a lifeline to new parents who rely on locally accessible advice and support at a time when it is most needed."
Cameron, 49, is the MP for Witney in Oxfordshire and the children's centre falls within his constituency.
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He had himself clashed with council leader Ian Hudspeth last year over the cuts to local services.
Jill Huish, who runs the campaign that Cameron's mother backed, said: "It shows how deep austerity is cutting our most vulnerable when even David Cameron's mum has had enough."
Downing Street has declined to comment on the issue so far.