Heritage Ottawa plans to file a lawsuit challenging the heritage permit that allows for Larco Investments to build the addition to the century-old heritage building.

The battle over the Chateau Laurier is expected to continue Tuesday as Heritage Ottawa is set to file a lawsuit.

The challenge will be against the heritage permit that hotel owner Larco Investments obtained by the city to build the seven-storey box shaped addition.

More detail on the lawsuit will come out once it's filed by the organization.

In a 14-9 split, council voted down councillor Mathieu Fleury's motion that would have voided the permit to build the addition to the century-old heritage building.

Following this, Heritage Ottawa's former president David Flemming had stated the group would look into what legal action it could take.

The decision not to halt development of the box shaped addition has drawn attention from the federal government, with Environment Minister Catherine McKenna pushing for the owner to come up with another plan for an addition.

Ottawa born actor and comedian Tom Green has also been vocal about the expansion, holding a protest picnic Saturday that 200 residents took part in.