Concerns have been raised that patients with VHI health insurance are now able to access new cancer drugs that are only available to public patients in limited circumstances.
Oncologists will be able to prescribe certain new cancer drugs for melanoma, breast cancer and lung cancer to private patients who are VHI customers, but not their public patients.
The HSE only funds the drugs for patients who are very advanced or at Stage 4 of the disease.
The Sunday Business Post reports that this is after the biggest health insurer in the country recently wrote to oncologists stating that it was extending access to new drugs for patients with certain cancers.
In a statement, VHI said it was committed to ensuring that its members can avail of new innovative treatments.
Some working in the field describe the move as unprecedented and "unfair".
Medical oncologist John Crown said he welcomes the move for VHI customers but is "personally very troubled by it".
He said: "For the first time since I can ever recall, we have a difference in access to cancer drugs between public and private patients. It's completely unfair. It's going to be extraordinarily difficult now."
Prof Crown continued: "I'll be seeing public and private patients this week and I will quite possibly be giving both of them different news about what treatment is available for them and I'm not comfortable with that."
The Irish Cancer Society has also weighed in, stating that patients without insurance must not be denied access to potentially lifesaving drugs.
Chief Executive Averil Power said it is "only right" that every patient should have the same access to drugs regardless of whether they are public or private.
The drugs are expensive and don't work for everybody, she said, but it could have a "huge benefit" for the patients for whom they do work.
The Irish Patients Association has also called on the Government to "immediately match public patients' access" to the medicines.
A statement from the association said: "This is another example of our two tier health system - where some public patients will die or have a lesser quality of health versus the outcomes for private patients who have more timely access to treatments and medicines."