With his private member's bill on union finances now in the Senate, Conservative MP Russ Hiebert is confidently predicting it can withstand a constitutional challenge.

Bill C-377 was passed by the House of Commons after it was amended to remove provisions dealing with pensions, and to make it less expensive for the government to implement.

A number of labour groups have predicted the bill won't stand up to scrutiny by the courts, but Hiebert insisted Thursday that the experts he consulted all say it is constitutionally sound.

"In drafting the bill, we brought it to a variety of constitutional experts in Canada, people who are ... experts in that field," he said.

"They assured us the way that it's drafted would sustain any constitutional challenge."

When pressed, however, Hiebert refused to disclose which experts he consulted, saying he didn't get permission to reveal their names.

Amends Income Tax Act

The bill, once passed into law, will force unions to publicly disclose how they spend the dues they collect.

It would amend the Income Tax Act to require unions to provide detailed annual financial filings to the Canada Revenue Agency, which would in turn make the information public.

The amended bill that was approved in the Commons will, however, hold back some personal information from public view for privacy reasons.

"I believe the bill that's been placed before the Senate is actually an improved bill," Hiebert said.

"Several amendments were made to C-377 ... that improve protections for individual privacy and reduce the cost of the bill to the government."

Prior to the amendments, the Canada Revenue Agency had estimated the legislation would cost over $20 million to implement and almost $4 million annually to deal with the financial files delivered by unions.