Call it the Rathgeber clause: Liberals in the Senate are seeking to amend a Conservative bill forcing disclosure of union expenses saying it ought to match another Conservative bill on disclosure of public sector salaries.

That bill had been sponsored by backbench Tory MP Brent Rathgeber and had sought the publication of which civil servants made more than $188,000 a year.

But then the Conservatives raised that bar to over $444,000, prompting Rathgeber to quit in disgust saying the bill had lost its bite.

Now the Liberals say if that threshold is what the government wants for public servants, why not unions too?

So Liberal Sen. Pierrette Ringuette has proposed an amendment to Bill C-377 that would see disclosure requirements raised from salaries over $100,000 to match the $444,000 bar set for public servants.

Union bill controversial from start

The union bill was introduced in 2011 by B.C. Tory Russ Hiebert, who argued that public disclosure of union expenses and salaries ought to be mandatory as union fees are tax-deductible.

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The bill passed the Commons late last year despite widespread opposition and the government had hoped to see it pass through the Senate before summer break.

But Conservatives in the Senate have raised questions as well.

The committee charged with studying the bill reported that it wonders whether the law is constitutional and said it is also concerned about the cost of implementation and the vagueness as to whom the legislation would apply.

And Tory Sen. Hugh Segal has also spoken out against the proposed legislation, calling it bad public policy and questioning the wisdom of dispatching revenue agents to monitor its implementation.