The Save Childcare Vouchers Campaign has become the second largest on the Downing Street website.
It was launched in response to the prime minister's announcement, at the Labour Party Conference last month, that his Government would offer more free childcare places for two and three-year-old children of low earning families, and fund this by reducing tax efficiencies on childcare vouchers for higher earning families.
Simon Moore, managing director of Computershare Voucher Services (formerly Busy Bees), said: "We've had a huge volume of parents calling and emailing us to ask if what they've heard about the phasing out of childcare vouchers is true.
"Many of them are concerned about how they'll be able to afford to carry on working, or indeed return to work."
Find the petition at: http://petitions.number10.gov.uk/keepvouchers/