Speaker Lockwood Smith is looking into how a last minute pre-election change saw former MPs' retain high taxpayer subsidised travel.
Former speaker Margaret Wilson put a limit on subsidised travel in 2007 which meant the level of discount for those still in Parliament was halted as at 2005.
The ruling was reversed before last year's election.
A spokesman for Dr Smith said he was "seeking information about the background of the whole matter and won't comment until he's had a chance to review the information".
In 2003, the Parliamentary Commission recommended members elected before 1999 have their entitlements frozen at the level they were at the end of that term of Parliament.
In November 2003, then speaker Jonathan Hunt issued a document setting out travel and other perks available to MPs.
It also outlined changes proposed for former members' entitlements.
"Current members elected before 1999 will have their retiring travel entitlements frozen at the level they qualify for at the end of this current term of Parliament," the document said.
This never happened.
In 2007, the next speaker, Margaret Wilson, issued a directive on the freeze.
"A person who was a member during the 2002-2005 parliament and who was also a member before the 1999 election has his or her travel entitlements frozen at the level for which he or she qualified at the end of the 2002-2005 term of Parliament."
But the 2008 Parliamentary Travel, Accommodation, Attendance, and Communications Services Determination overturned it.
The determination would "remove the freeze on former members' travel rebates in respect of parliamentary terms after the 2002-2005 parliament."
As a result, travel perks were restored to 23 MPs, 12 of whom were not re-elected.
Present and former MPs elected before 1999 receive a 60 percent discount on travel after nine years of service; after 12 years they get 75 percent; after 15 years they get 90 percent.
Former cabinet minister Sir Douglas Graham has said he would not give up his travel allowance, though he would swap it for a pension when he got too old to travel.
Sir Douglas said he had "absolutely" used the 90 percent travel discount he was entitled to.
When details of MPs' expense claims were released for the first time last month, ACT MP Sir Roger Douglas came under fire for using the discount to fly himself and his wife to Britain.
