The Pro-life Action Network, which claims it can call on the help of up to 20,000 supporters, will hold prayer vigils outside the new Marie Stopes day centres - which it describes as "machines of destruction".
It promised to step up its campaign in the light of the launch by Marie Stopes International of the centres in London, Leeds and Manchester which offer abortions "that could easily be completed during a working woman's lunchtime break".
The stark marketing of the centres caused uproar among anti-abortion campaigners and drew criticism from Tessa Jowell, the health minister, who said the launch had trivialised abortion.
The method of termination, by suction, has been used by gynaecologists since the early 1970s but this is the first time it has been offered in Britain as part of a convenience service outside hospitals or clinics.
Launching the service, Dr Tim Black, the charity's chief executive, chilled many observers with his description of the method as the "minimal service interception technique", a "seamless service without medical drama or moral censure" and a "quantum leap in service delivery".
In response, Kinga Klepacka of the Pro-life Action Network said: "We shall make a point of attending all these new clinics because they represent an increase in the rate of destruction.
"We shall hold prayer vigils and speak to women going in and out if they want us to." She said past vigils had been successful in "sparking the consciences of women" who have subsequently turned around and gone home.
Yesterday, Ms Jowell, who approved licences for the day centres in May after two years of negotiation, accused Marie Stopes of "trivialising" abortion. "The new service is to be welcomed and is a service which will operate very clearly within the context of the 1967 Abortion Act," she said. "However, I believe that remarks that were made that appear to trivialise the importance of a decision to have an abortion are unfortunate and have distracted attention from the welcome that is due to a modern, safe, sensitive service."
Cardinal Basil Hume, the Archbishop of Westminster, criticised the move. "It seems to me that a decision about human life and death is increasingly becoming a matter of trivial and routine choice. Society must reflect upon the inhumanity of conniving in what appears to be a 'walk-in walk- out' abortion service."
But Dr Black was unrepentant yesterday. He said abortion had been made legal in Britain 30 years ago: "Why 30 years later is there this preoccupation of making women have to climb over fences and do back-flips and censure them, if they want to have an abortion?"