A major showdown is about to begin in the House of Commons as opposition members try to delete parts of a massive 425-page omnibus bill – or at least delay its passage – and bring more attention to the many changes it will make to a broad swath of Canadian law.

Liberal House Leader Marc Garneau told reporters Monday the hundreds of amendments his party and the New Democrats have proposed to delete parts of the bill could take close to 30 hours of voting – a round-the-clock effort that is expected to begin late Wednesday.

In addition, Green Party Leader Elizabeth May has introduced more than 300 of her own "substantive amendments" to Bill C-38, many of which were written with the support of the Liberals and the New Democrats. Those could take an extra days couple of days.

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But House Speaker Andrew Scheer later opted to group many of the amendments, which means voting can likely be completed within a single day.

Mr. Garneau said the opposition tactics this week are a good use of Parliament's time even though the Conservatives hold a majority and the bill is likely to be passed unaltered.

"I watched people discussing this on the weekend and actually we are being praised for holding the government up to its democratic obligations," Mr. Garneau said.

"Yes, we all know what the outcome is if they don't fall asleep at the switch. But it sends a very, very strong message to Canadians that this government just bulldozes through and is not prepared to do what is very reasonable which is to break out some of these parts of the budget that really are not part of the budget implementation process."

Ms. May said Bill C-38 is the "most egregious" piece of legislation ever tabled in Canada and the government has grouped all of the disparate measures together in one bill for no other reason than to avoid scrutiny. It is an "attack by stealth" on 70 different laws and many sections have no connection to the budget, she said

"It's not as though for efficiency's sake, [Prime Minister] Stephen Harper wants all laws compressed into one omnibus bill all the time," Ms. May told reporters. "The ones he doesn't want you to notice are compressed in an omnibus bill."

The Conservatives will have to ensure they have enough of their members in the House around the clock to prevent the passage of any of the amendments. Because Bill C-38 is a budget bill, they could all be considered matters of confidence.

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Opposition MPs have demanded the government break the bill into smaller chunks for more in-depth analysis. The Conservatives have refused to do so, arguing the legislation is essential for the prosperity of the Canadian economy.

But the opposition MPs counters that many of the 753 causes have nothing to do with the federal budget – or economic growth.

The Liberals would like to hive off four main areas Bill C-38. The first deals with the environment. Clause 52, for example, is an entire act in itself called Canada Environment Assessment Act 2012, Mr. Garneau said. "To put all of this in one clause in a budget implementation bill is totally unacceptable."

The second area the Liberals want taken out deals with fisheries. "There are changes to the Fisheries Act that will have impact to coastal areas, to coastal economies, and this bill is important enough that the clauses dealing with fisheries should be broken out of Bill C-38," Mr. Garneau said.

The third section they want removed deals with Old Age Security. The government intends to raise the age that Canadians can collect OAS to 67 from 65. But, according to the bill, this will not happen for 11 years. "So the argument of urgency does not apply here," Mr. Garneau said.

And the fourth section deals with changes to Employment Insurance.

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"We won't fight other issues," Mr. Garneau said. "We have 753 clauses here. We have left 250 in there. Those deal with budget implementation. We have no problem with that. But these four areas are particularly important."

The Green Party Leader was hard pressed to say which sections of the legislation she found most offensive. But her amendments, she said, have taken the government's intentions into consideration.

For instance, Ms. May said, they would help streamline environmental assessments and introduce timelines but would not destroy the process altogether. Her amendments are not tactics, she said, but when the government introduced a bill that is this long, it can expect hundreds of amendments.