Plans to merge NHS Hospital Trusts in Dorset will be investigated by the Competition Commission.
Proposals have been made to merge Poole Hospital Foundation Trust and The Royal Bournemouth and Christchurch Hospitals Foundation Trust.
The Office of Fair Trading announced the plans had been referred to the Competition Commission, with the decision welcomed by the Foundation Trusts.
Tony Spotswood, proposed chief executive of the merged organisation said: "We are pleased that we are one step further in this delicate process and that the Office of Fair Trading has undertaken the predicted step to refer our proposal to the Competition Commission.
"There will now be a period of further analysis, which we anticipated, being the first Foundation Trusts in the UK to follow this process.
"It will hopefully reassure us all that a merger is indeed in the best interests of patients and staff.
"We look forward to working with the Competition Commission over the coming months."
The Competition Commission will examine whether the proposed merger would result in substantial lessening of competition.
A final report is expected to be published by June 24, 2013. Anyone wishing to submit evidence should be so in writing before January 29.