Irving Pulp and Paper has served notice it will launch a Charter challenge against a water pollution test used nationwide for decades.

The company is alleging the 'acute lethality test' is unconstitutional.

The test places live fish in a tank of pure pulp mill effluent for 96 hours.

If more than 50 percent of the fish die, the effluent can be considered a 'deleterious substance'.

In the case of the pulp and paper industry, the test is performed by the companies involved and is self-reported.

In December Irving Pulp and Paper was charged with 15 counts of violating the federal Fisheries Act by dumping a harmful substance into the St John River over a two year period from June 2014 through August 2016.

The company has pleaded not guilty.

The nature of the substance has not been revealed.

In a Notice of Motion filed with New Brunswick's Provincial Court, the company alleges: "The mere failure of an [acute lethality test] in a laboratory is not determinative of potential harm to an actual fishery."

"The ALT is not a reliable predictor of whether effluent actually poses any harm to fish in the natural environment," the motion says.

The notice goes on to say the practice exposes people involved to being convicted of "significant fines, and potential imprisonment, even though such effluent does not pose any harm to an actual fishery."

The notice says Irving Pulp will argue the federal government, in charging the company, has acted outside its authority, and further that the charges are over broad and vague.

The launching of a Charter challenge by the company is upsetting for Matthew Abbott of the Conservation Council of New Brunswick.

"I'm wondering why not just comply with the law?" Abbott said.

"There almost seems to be a claim here by Irving that they have the freedom to pollute. I don't think that's the case. And they seem to think they should only face consequences once someone has been able to prove conclusively that a harm has occurred."

Abbott says the Fisheries Act is meant to be preventative.

He says it's set up that way because plumes of pollution are often invisible and it's difficult to follow and measure impacts.

Court dates for the case are to be set Oct. 19.

A spokesperson for Irving Pulp and Paper said it would not be appropriate to comment with the matter still before the courts.

It is expected the trial will take six weeks and will unfold in mid-to-late 2018.

Because of previous pollution convictions in 2007, the company faces a minimum penalty of $3 million if found guilty.