Canada's largest public service union is under fire from members who are questioning a plan to increase pensions for union executives.

Senior union executives with the Public Service Alliance of Canada are highly-paid, often earning salaries higher than what they made when they worked in government -- some of them well into the six-figures.

The new plan is designed to supplement their pension between their old government job and their current higher salary with the union.

But union members are worried the supplemental pension plan for PSAC executives could cost members millions of dollars from their strike fund.

"There's no other money available, just the contingency fund they're going to dip into, which is going to affect every employee under PSAC's umbrella," said union member Glenn Standen.

Although some members are upset, the president of PSAC is defending the plan as a way to give union executives what everybody else is getting.

"It's no more, no less than if you were working in federal public service. It's what our members get right now," said union president John Gordon.

However, the move to boost pensions for union executives comes as members adjust to a new collective agreement, in which they gave up their lucrative severance pay in exchange for a pay raise. It was a contract that only half the membership voted for.

Standen says his questions about the supplemental pension plan got him threatened with disciplinary action and caused him to be shut out of the PSAC Facebook site. Other members told CTV Ottawa they weren't allowed to talk.

The national board of directors with PSAC voted on this issue in early February. In a narrow vote, the resolution passed.

A document leaked to CTV Ottawa indicates a start-up date of March 1. The projected cost is between $4 million and $18 million.

However, Gordon says details still need to be worked out on how the plan will be funded -- if indeed the plan goes ahead at all.

"There is no expectation that union dues will go up as a result of this, but that will be discussed at convention," said Gordon.

PSAC has a major convention planned for next year where members say this issue will be front and centre.

With a report from CTV Ottawa's Joanne Schnurr