Some doctors are breaking the law by "pre-signing" abortion consent forms, the government has said.
Spot checks at more than 250 abortion clinics this week found evidence of blank forms being signed in anticipation of patients seeking a termination.
The law states that, except in emergencies, two doctors must agree for a woman to have an abortion.
Although doctors do not have to see the woman in person, they must certify that they are aware of her circumstances and why she wants to go ahead with the procedure.
Nurses, counsellors and other healthcare professionals can assess the woman before the forms are signed.
The inspections in England, by officials from the Care Quality Commission (CQC), were ordered by the health secretary, Andrew Lansley.
Of more than 250 clinics investigated so far, it is thought 15% to 20% may be breaking the law.
The clinics included those run by the British Pregnancy Advisory Service (BPAS), Marie Stopes, the NHS and private firms.
Marie Stopes said none of its 19 units was found to have breached the rules, while BPAS said that to the best of its knowledge none of its clinics was involved.
Lansley said: "I am shocked and appalled to learn that some clinics - which look after women in what are often difficult circumstances - may be allowing doctors to pre-sign abortion certificates. This is contrary to the spirit and the letter of the Abortion Act.
"The rules in the Abortion Act are there for a reason - to ensure there are safeguards for women before an abortion can be carried out. To protect women the right checks and balances must be in place.
"The CQC has agreed to undertake unannounced inspections to identify the scale of this problem. And we will set up a special team comprising of all the necessary regulators and the department to look at how we stamp out bad practice in abortion clinics."
The news comes after a Daily Telegraph investigation last month uncovered allegations that doctors at three clinics had agreed to terminations based on the sex of the baby.
The General Medical Council (GMC) has suspended or placed restrictions on these doctors and the claims are being investigated by the Metropolitan police, Greater Manchester police and West Midlands police.
The chief executive of BPAS, Ann Furedi, said she was appalled the media had been told about the latest inspections before the clinics.
She said: "Abortion doctors provide an important service to women who are often in difficult circumstances.
"Their work is already intensely scrutinised, with clinics regularly inspected by the Care Quality Commission.
"Mr Lansley says he is shocked and appalled by the practices he has uncovered.
"BPAS is shocked and appalled that Mr Lansley has found it necessary to inform journalists of alleged breaches of the abortion law before he has informed those responsible for providing the services that have been investigated, and before the investigation is concluded."
A statement from Marie Stopes said it fully supported "the desire of the Department of Health and others to ensure that women seeking termination of pregnancy from any provider - including the NHS - receive care which is appropriate and falls with the legal framework.
"We are pleased that all of our facilities were working with this legal framework."
In the UK, abortions are allowed on certain grounds, including that continuing with the pregnancy would be a greater risk to the woman's life, physical or mental health than ending the pregnancy, continuing would be more of a risk to the physical or mental health of any of the woman's existing children and there is a real risk the child would have a serious physical or mental disability.
In September, Conservative backbencher Nadine Dorries and Labour's Frank Field lost a Commons vote on the issue of counselling.
They wanted to prevent abortion providers such as Marie Stopes and BPAS from offering counselling.
Dorries said that, because they receive money for carrying out terminations, the organisations have a vested interest.
A cross-party abortion group was set up by the government to look at the issue of counselling following the defeat. It is formulating proposals for consultation, which could include stripping providers of their existing role.
