Fears have been raised that NHS Shetland and Orkney could be “mothballed by further top-down SNP centralisation”.
Northern isles MSPs Tavish Scott and Liam McArthur warned ministers they would have a “fight” on their hands if they attempted to merge or scrap the health boards.
The Scottish Government’s Programme for Government, launched last week, will “begin work to examine the number, structure and regulation of health boards, as well as their relationship with local authorities”.
Public Health Minister Aileen Campbell insisted the administration’s commitment to island communities is “unrivalled”.
Mr McArthur and Mr Scott have now written to Health Secretary Shona Robsion seeking assurances on the future of the northern isles health boards.
In a joint statement, they said: “Centralisation of public services has been relentless over recent years, and at the expense of local services where NHS boards in both Orkney and Shetland already face additional costs in providing care to remote island communities.
“Ministers don’t know best, and a one-size-fits-all approach rarely works for island communities. Health care in Orkney and Shetland more often than not requires different solutions to the central belt.
“Patient travel to Aberdeen for a range of medical needs is just one example of the difference.
“If ministers believe that the answers to these challenges is squeezing budgets and ever-greater central control then they will have a fight persuading the communities we represent.
“People in Orkney and Shetland want assurances that their local health boards will not only be protected in a government review, but properly resourced to provide the best possible health care.”
But Ms Campbell dismissed the MSPs concerns.
She said: “As was set out in the programme for government we will begin work in this parliament to examine the number, structure and regulation of health boards, as well as their relationship with local authorities, so that we can reduce bureaucracy and remove any barriers to effective patient care.
“This review has not yet begun, but our commitment to Scotland’s island communities is unrivalled and any final proposals will be consistent with our aim to ensure their unique needs are reflected.”