A petition protesting against Pope Benedict XVI's visit to Britain later this year is to be handed in to Downing Street by the National Secular Society.
It calls on the prime minister to exempt taxpayers from funding the visit.
It will be the first papal visit to the UK since John Paul II in 1982.
He is expected to visit Birmingham - as part of the planned beatification of Cardinal John Newman - and Scotland. Dates for the trip have not been set.
The Pope was formally invited to visit the UK by Prime Minister Gordon Brown last February. Scottish Secretary Jim Murphy also invited him to visit Scotland
The petition states: "We the undersigned, petition the Prime Minister to ask the Catholic Church to pay for the proposed visit of the Pope to the UK and relieve the taxpayer of the estimated £20 million cost.
"We accept the right of the Pope to visit his followers in Britain, but public money would be better spent on hard-pressed schools, hospitals and social services which are facing cuts."
The National Secular Society says that 28,000 people have now signed their petition.
BBC religious affairs correspondent Robert Pigott said Roman Catholics were trying to improve the way they get the Church's message across to an increasingly sceptical public in preparation for the visit.
Articulate Catholics are being trained as spokesmen and women to answer some of the awkward questions about contraception and Aids, homosexuality, and the meaning of sainthood in the 21st Century that his visit is likely to prompt.
He said they know the visit represented a great opportunity, but also something of a danger.
Pope Benedict is a relatively conservative figure who has not been afraid to reinforce the Church's traditional teaching on controversial issues such as abortion, equality for gay people and research on stem cells.
Our correspondent said: "So secularists have also spotted an opportunity. They can see the potential for creating a coalition of people unhappy with the traditionalist Christian message in a variety of limited fields.
"The Pope might not exactly be a stick with which to beat religion, but his visit will focus attention on areas which the National Secular Society suspects will inspire scepticism as much as faith."
No official itinerary has yet been drawn up for the visit, but officials at the Vatican and in the UK told the BBC the visit was likely to take place in September.
Further details are expected early in March, a spokesman for the Catholic Communications Network said.