Prime Minister Key said it wasn't standard for MPs' partners to have their travel paid for.
Mr Key said when Bronagh accompanies him overseas they pay her expenses.
"I think generally in terms of the Speaker's tour itself there is some merit in that [having politicians travel]...there is always merit in developing connections and relationships overseas."
Partners are a bit of a different issue but I there will be some historic reason for that."
Mr Key said it was not his office's call on whether the rule on partners' travel being paid for should be changed.
Mr Carter will lead the trip and said the visit was an opportunity to meet political leaders and strengthen some of New Zealand's "oldest and most significant contemporary relationships with European countries".
The delegation would also mark important and historic commemorations, including the 98th anniversary of the Battle of Arras in France and the 70th anniversary of the liberation of the Auschwitz Nazi concentration camp.
Accompanying Mr Carter will be National's Deputy Speaker, Chester Borrows, first-term Labour MP Adrian Rurawhe, Green Party foreign affairs spokesman Kennedy Graham, first-term New Zealand First MP Fletcher Tabuteau, and two parliamentary staff.
All the MPs except Mr Rurawhe are bringing their partners, whose costs were covered by Parliamentary Relations, part of the Office of the Clerk of the House.
Parliamentary Relations manager Steve Cutting said the budget for the tour was $138,000, of which $97,000 was for business-class flights.
Some of the costs would be met by the Parliaments of Poland and Germany, which had invited the Speaker to attend events in their countries.
Mr Cutting noted that the estimated budget was less than in previous years. The 2012 Speaker's Delegation to Britain, Croatia and Belgium cost $158,000.
The official itinerary showed the MPs would begin their tour in Arras, where they will visit a memorial for 41 New Zealand soldiers killed while constructing tunnel networks for the Allies.
They will then meet trade officials, economists and the French parliamentary Speaker, and visit the OECD headquarters and chateau in Paris.
Later, they will dine in Dublin with honorary consul-general Alan McCarthy and High Commissioner Sir Lockwood Smith, before touring the Irish and Northern Irish Parliaments and visiting the birthplace of former New Zealand Prime Minister John Ballance.
The following week they will meet the Polish Deputy Prime Minister, Janusz Piechocinski, in Warsaw and visit the royal castle and Wawel Cathedral in Krakow. MPs will then visit the Auschwitz death camp before travelling on to Munich and Berlin for further meetings with officials and dignitaries.
Among other staff, first-term New Zealand First MP Fletcher Tabuteau will be accompanying David Carter.
Dr Graham referred questions about the trip to the Speaker's office. Mr Tabuteau, Mr Rurawhe and Mr Borrows were travelling and could not be reached.
Mr Carter said the New Zealand delegation would "exchange views on the significant economic, political and security challenges in the European Union and its near neighbourhood, as well as those affecting the Pacific".
The statement continued: "The delegation will also discuss and learn each country's perspectives on recent developments within the EU, particularly for European economies and in the area of immigration."
Speaker's tour
April 8-23
MPs: David Carter, Chester Borrows (National), Adrian Rurawhe (Labour), Kennedy Graham (Greens), Fletcher Tabuteau (NZ First)
Destinations: France, Ireland, Northern Ireland, Poland and Germany
Flights: $97,000
Accommodation: $21,000
Transportation: $5500
Interpreters: $3000
Meals and other incidental costs: $11,500
Total: $138,000
