Forty-three maternity units across the UK are under threat, the Conservatives have warned.
Women should be offered a choice over where they give birth by 2009
They say 21 midwife-led units and 22 run by consultants have either closed or may do so.
Most are in England, and two-thirds are in Conservative, Liberal Democrat or Independent seats, the analysis of the possible closures finds.
But the Department of Health challenged the figures, saying safety and quality demands meant services must change.
Of the midwife-led units the Tories claim are under threat, 16 are operated by trusts which finished the 2005-06 financial year in deficit.
Out of the 22 consultant-led units, 11 are run by trusts which had a deficit.
The Tories compiled their figures from Royal College of Midwives data and from press reports.
They say some closures or downgrading of units will be justified by local needs, but many were being driven by the need to address deficits.
The Tories are now starting a consultation to discover where local health staff and patients are concerned about planned cuts.
Shadow Health Secretary Andrew Lansley said: "Maternity units are the latest frontline service to bear the brunt of Labour's financial mismanagement of the NHS.
"The government talk about delivering choice to mothers, but cutbacks are taking that choice away.
"There is little logic behind these reconfigurations - the only pattern appears to be that units with fewer than 3,000 births a year are being targeted for closure.
"Once again, the consequence of deficits is that accessible local services will be denied to patients."
The government has pledged that, by 2009, every woman should be offered the choice of planning a birth at home, in a midwifery-led unit, or in a consultant-led unit.
A Department of Health spokeswoman said: "Our current figures show that 14 maternity units have either been closed, are due to be closed, or will become a midwife-led service."
She added: "It is contradictory to argue for operational independence in the NHS and then portray every proposed change as a cut.
"What matters in every part of the country is that we ensure families have access to safe, high quality maternity services which offer real choice.
"In some areas this will mean that the reconfiguration of services is not only essential but the only responsible course of action to be taken by those running the NHS locally.
"It is the quality of service, locality by locality that matters, not the number of units."
A spokeswoman for the Royal College of Midwives said: "We accept changes are necessary to provide high-quality care, but we will challenge cuts on behalf of women whose choice would be unduly restricted.
"And we are concerned that the financial situation seems to be having a detrimental effect on the choices for pregnant women and their families."
'Close to home'
Mary Newburn, head of policy research for the National Childbirth Trust, said there were a number of factors which were affecting the future of doctor-led units.
"There are NHS trusts which have a big deficit and which have been told they must take action to tackle that."
But she said changes to trainee doctors' working hours, because of the European Working Time Directive, were "likely to be more of a factor in many hospitals' decisions about maternity services than money".
"Some of the smaller units that have relied on junior doctors providing medical cover cannot continue to do so.
"That means they have to be staffed by qualified doctors and, hence, the service becomes more expensive.
"That's one of the factors driving reconfiguration."
She added: "We are also concerned that 'concerns' over the safety of staffing levels have been used as a back-door way of closing midwife-led units."