The new figures have been released under the Freedom of Information Act.
Tax-payers have paid more than €2.9 million euro for pre-paid envelopes for TDs and Senators in the past three years.
Last year Oireachtas members used more than 1.1 million of these envelopes.
The new figures have been released under the Freedom of Information Act.
A TD is entitled to 625 letter size pre-paid envelopes a month, while a senator is entitled to 375.
They can be used for responding to queries from constituents, but not for campaigning or party purposes.
This cost more than €947,000 euro last year and just under 1 million euro in both 2017 and 2018.
Last year 63 TDs claimed their full allowance, including Taoiseach Leo Varadkar, Tánaiste Simon Coveney, Laois Minster Charlie Flanagan and 10 other cabinet ministers.
The only senior ministers who didn't use their full batch of envelopes last year were Shane Ross and Katherine Zappone.
Dara Murphy quit as a Fine Gael TD in December, and for the two years before, he was controversially based mainly in Brussels.
The new figures show he claimed his full allowance of Oireachtas envelopes between January and November of last year.
Three Westmeath Senators, Fine Gael's Gabrielle McFadden along with Fianna Fail's Aidan Davitt and Paul Daly, were among the 24 members of the Seanad who claimed their full allowance last year.
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