In one case, Senator Scott Tannas of Alberta billed $12,000 to taxpayers to fly himself and his wife in executive class to Ottawa for a two-day trip.
Another senator, from Toronto, was one of the party's highest billers for travel despite being just an hour by air from the national capital.
The pricey travel, found by a CBC News review, came at the same time as senators were debating whether or not to suspend three of their peers — Pamela Wallin, Mike Duffy and Patrick Brazeau — for questionable spending practices.
"To me, it's really shocking that they exercise such poor judgment, even if it's legal," said Ian Greene, a professor of public policy and administration at York University in Toronto. "I would think, because such bad judgment has been exercised, it would be important to get expenses approved in advance by someone, maybe a senior member."
CBC News reviewed voluntary online expense reports posted to Conservative senators' websites for the same five-week period, from October 14 to November 17.
During those five weeks, three of the top four Tory travel spenders in the Senate claimed a total of $24,011.79 on business class airfares for themselves and another $13,719.21 on business class flights for their spouses.
CBC News could only review expense reports for Conservative senators. Detailed expense claims for former Liberal senators and Independent senators haven't been made public yet, though Liberal Party promised they would be posted soon. Conservative Senator Pierre-Hugues Boisvenu has also not made his voluntary disclosure available yet.
Senate travel rules restrict the number of flights a senator can take each year, but place no limit on how much a senator can spend on each airline ticket.
According to the Senators' Travel Policy adopted in 2012, senators are allowed to fly business class. They are also warned to use good judgment.
"Spending public funds on travel is a sensitive matter and sound judgment must be exercised when travel-related decisions are made," the policy says.
"It is expected that decisions to incur travel expenditures will be made with due regard to the need, frequency, cost and purpose as it relates to a senator's parliamentary functions."
The policy allows spouses and family members to travel with senators to Ottawa in business class and at taxpayer expense for "family reunion" after a lengthy time apart.
"This policy also recognizes that a senator's parliamentary functions can result in frequent and lengthy periods of separation from family," the document says. "In that context, the policy provides for family-reunion travel as an important contributor to the health and well-being of senators and their families."
Senator Tannas embarrassed
In the period the CBC reviewed, Alberta Senator Tannas — who voted in favour of suspending Wallin, Duffy and Brazeau for spending abuses — was the top Conservative Senate travel spender by a large margin. In five weeks, he claimed more than $24,000 for himself and his spouse.
"I think that you've picked the absolute worst possible month in which to highlight my expenses, and I stand behind them embarrassed," Tannas said in an interview.
"But I know that over the course of the months that have occurred since and will occur in the future, that those numbers will come down substantially. Some of that by virtue of just gaining experience here and knowing how to manage travel better."
Tannas, a successful Alberta businessman before joining the Senate in spring 2012, said his travel expenses were unusually high because he's new to the Senate. He and his staff didn't know they could save money on travel by purchasing airline tickets in bulk, Tannas said.
The cost of Tannas's round-trip business class flights from Calgary to Ottawa and back ranged from $2,400 to just over $5,600. On one trip, both he and his wife flew business class on tickets costing just over $5,600 each.
"I must be the prize winner on the flight for getting to buy the most expensive seat. I wasn't insisting on paying that kind of money, but that's what was available at the time," Tannas said. "So we consulted with some other senators and found out people were using flight passes and you buy them in books of 10 or 12 or something and it reduces the cost."
Tannas said he will continue to fly in business class because it's allowed and he will continue to fly his wife to Ottawa using public money. He said he was not aware of a policy that specifies spousal travel must be for the purposes of a "family reunion."
"This really beats the $18 glass of orange juice," Prof. Greene said, referring to the controversy over former international co-operation minister Bev Oda, who expensed a costly glass of orange juice while at a conference in England.
"It is extraordinary when they could have done it for much less than that."
Senator Plett: 'Nothing wrong intentionally'
Manitoba Conservative senator and former Conservative Party president Donald Plett claimed the second-highest amount of money on travel during the five-week period reviewed by CBC News.
In total, Plett spent just over $12,000. He was not in favour of suspending the three senators whose fate was being debated at the time.
The cost of airline tickets between Winnipeg and Ottawa purchased by Plett ranged from $1,300 to as high as $3,000. He also flew his spouse to Ottawa using public money three times at a total cost of nearly $6,000.
"I will be audited along with all my other colleagues. So I am not going to comment until after the audit is complete," Plett said in an interview.
"I know that the audit will find that I have done nothing wrong intentionally," he added. "Am I going to have some mistakes? I've been here for 4½ years and it is a fairly complex system at times and certainly I will not comment on whether there have been some mistakes made, but I will not have intentionally done anything wrong."
'In line with our regular expenditures'
Toronto-based Conservative Senator Don Meredith rounds out the top three highest Conservative spenders on spousal travel.
He was one of the few senators who abstained from the vote to suspend Wallin, Duffy and Brazeau.
Overall, Meredith was the fourth-highest spender on travel out of all Conservatives in the upper chamber — even though he is based in Toronto and has one of the shortest distances to travel when flying to Ottawa.
"It's shocking because there's no need to travel business class between Toronto and Ottawa," Greene said. "And to travel with that amount of frequency shows very bad judgment."
The cost of Meredith's business class return tickets between Toronto and Ottawa, a one-hour flight, ranged from $1,100 to $1,400. The same ticket in economy class can be purchased for as little as $400.
Meredith defended his spending decisions when approached by CBC News.
"We travel according to the plan that is given to us," he said. "It is up to us to be able to travel. Sometimes I do take the train up to Ottawa when it is necessary to do so. But I do travel from Toronto just like the rest of my colleagues travel, through Air Canada, and I am happy to do that and they are in line with our regular expenditures."
His spouse travelled with him to Ottawa twice in the five-week period reviewed by CBC News at a total cost of just over $2,500. It's a perk Meredith said many senators take advantage of.
"Absolutely. All senators, their spouses if they come to Ottawa, they travel with them."
Greene, the public policy professor, said the rules around travel spending for senators are just too vague. Over the years, he said, that's likely resulted in one of two possible realities.
"One is that in the past, senators could be trusted not to lavishly spend in terms of expenses, and most exercise good judgment," Greene said. The second possibility? "It could be that it's been going on for a long time and continued because they could get away with it."
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