Almost 7,000 pensioners lost their medical cards in September - representing a fall of 2%.
New figures show that 6,838 fewer medical cards were held by people aged over 70 at the start of October compared to the start of September.
The figures were released in response to written Dáil questions from Fianna Fáil health spokesman Billy Kelleher.
He is calling for an urgent statement from the Taoiseach Enda Kenny to explain why so many cards were cut in a single month.
Mr Kelleher said: "Once again we see this government targeting vulnerable older people as it attempts to bring a flawed health budget into line."
"There was a significant acceleration in the number of over medical cards being removed from over 70s in September, raising concern about the scale of the cuts to come."
"In one month alone Enda Kenny's government has deprived almost 7,000 over 70s of the peace of mind that a medical card brings. It is an astonishing betrayal by the Taoiseach and should be addressed as a matter of urgency," he added.