They say the bill is supposed to be budget legislation, but much of it deals with changes to the environmental assessment process.
This element, they say, should be studied by the House of Commons environment committee, but the bill is going before the finance committee.
New Democrats say they will bring a motion before the Commons urging that the bill be broken up.
The Conservative majority can easily defeat such a measure.
The government is anxious to get the bill enacted as quickly as possible and has brought in time allocation to limit debate.
NDP House Leader Nathan Cullen says the government is doing the wrong thing.
"The whole bill is inappropriate," he said. "Let's take a look. It's supposed to be a budget implementation act, but two-thirds of the bill deal with environmental measures."
Finance critic Peggy Nash called the bill a "Trojan Horse."
"The way this bill is structured, this omnibus bill, it prevents the experts from examining this bill in a detailed fashion. It provides us much less information to make our decision.
"We can only wonder, is that because Conservatives think they'll get some answers that they don't like?"
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