Patient safety is being compromised by financial and target-driven motives, according to the shadow health secretary, Andrew Lansley.
Figures from the Conservative Party show that the number of people readmitted to hospital as emergency patients has increased by nearly a third since 2002.
Mr Lansley told the Today programme that the government's decisions regarding the NHS are partly to blame for this rise.
"I suspect it may in part be because the changes the government has brought in, in particular their emphasis on waiting time targets, are pressing hospitals very hard to discharge patients very quickly", he said.
"Now in some cases that is the right thing, but if it goes too far and patients are discharged at a point where there is too great a risk of their readmission it is not in the interest of the patient."
He added that due to the "big increase in readmissions" the issue needs to be investigated further.
"I don't think it is likely to be clinically justified, I think it may well be because hospitals are being pushed by the government, and maybe the payments by results system as well, to discharge patients quickly for financial and target driven reasons." Mr Lansley said.
Responding to the figures, Steve Webb, Liberal Democrat health spokesman, said that the current financial state of the NHS is forcing doctors and managers to cut the length of time that people spend in hospital.
"These figures show what can happen when financial pressures get in the way of clinical priorities," he said.
"It is a false economy to send people home too soon only to have them readmitted at a later stage."
A spokesman for the Department of Health defended government targets and insisted that they have "helped deliver a better service for NHS patients".