The battle over the memorial to victims of communism is heading to Federal Court after a coalition of architects and heritage advocates launched a legal challenge.

The move comes a day after the board of the National Capital Commission, a Crown corporation, voted 6-3 to allow Public Works to start digging up the planned site to decontaminate the soil.

The legal challenge claims this goes against a provision of the National Capital Act that states work can't begin on a project until it has received final approval from the board.

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The application to the Federal Court is being launched by the Royal Architectural Institute of Canada, Heritage Ottawa and architects Shirley Blumberg and Barry Padolsky.

While Public Works is responsible for the decontamination work, the office of Canadian Heritage Minister Shelly Glover responded to the legal challenge on behalf of the government.

"In spite of this new action in court, our government's view regarding the monument has not changed," said Marisa Monnin, a spokeswoman for the minister, in an e-mail. "This memorial will honour the more than 100 million lives lost under communist regimes – and pay tribute to the Canadian ideals of liberty, democracy and human rights."

At a public board meeting Thursday, the NCC unveiled new plans for the monument that respond to concerns about its size. Rather than taking up 60 per cent of a square near the Supreme Court of Canada, the latest plans have been reduced to 37 per cent. Further reductions are expected to bring it down to about 33 per cent of the square.

The peak height of the monument has also been reduced from 14 metres to eight metres.

However the NCC and the government are not backing down in the face of concerns over the location of the monument.

Critics say the site has already been designated under a long-term plan approved by Parliament as the location of a future Federal Court building.