The Halifax Port Authority says it will fight a proposed stormwater rate put forward by the city’s water commission on the grounds that it’s unconstitutional.

According to a letter to the Utility and Review Board the authority will legally challenge the fee if the board approves it later this month.

"Halifax Regional Water Commission and Nova Scotia Utility and Review Board lack the legislative and jurisdictional competence to impose what superficially appears to be a ‘regulatory charge’ but is in substance a tax," wrote lawyer Douglas Lutz.

Halifax Regional Water Commission is asking for a 30 per cent increase in water fees in the next two years, despite seeing a decrease in water consumption at the average home. It’s looking to increase both its stormwater and waste-water rates.

The utility is making the request to cover soaring repair bills for aging infrastructure. It's estimated Halifax Water is facing a $2.6 billion bill for its upgrades to the outdated water and sewer system.

Lutz  argues the utility board cannot levy a tax on the port authority.

"Neither HRWC nor the UARB can require HPA, a federal entity, to pay fees, charges or a tax, the purpose of which is to operate and maintain a system of stormwater management within HRM streets and roads," wrote Lutz.

The fee still must be approved by the Utility and Review Board.

The proposal has also upset some businesses.

Oland Brewery told the Utility and Review Board it may not be able to compete with plants in other cities if it has to pay as much as $1 million a year more.

A public hearing on the proposed rate increases will take place April 15.

It’s estimated the increase will bring the average water bill to $842.87 a year for homeowners in 2014.