Four women who sailed to Canada on the MV Sun Sea and spent their first month in the Great White North behind bars will soon be set free.

A Federal Court judge has dismissed Ottawa's attempt to keep the four Tamil migrants in detention.

The women were ordered released by the Immigration and Refugee Board earlier this week, after the board ruled the federal government wasn't moving quickly enough to confirm the women's identities.

The government asked the Federal Court to overturn those decisions but Judge Yves de Montigny ruled Friday the women can't be kept locked up indefinitely without sufficient evidence.

"Deprivation of liberty ranks no doubt as one of the harshest measures that may be visited upon an individual in a democratic state," the judge said.

"If stays were to be granted repetitively on the basis of a low threshold for establishing a serious issue, the respondent could be deprived almost indefinitely of the benefit of a release order."

A lawyer for the Minister of Citizenship and Immigration had argued each woman's identity had not been definitively established, justifying continued detention.

De Montigny said while identity is the lynchpin of Canada's immigration system, the women can't be jailed any longer without any proof they're security or flight risks.

The MV Sun Sea docked in British Columbia Aug. 13 carrying 492 Tamils.

Each of the women travelled with family members who are still being detained and de Montigny repeated the refugee board's point that it's in the women's best interests to comply with Canadian immigration law.

All four have filed refugee claims.

In one of the women's cases, government lawyer Helen Park had argued the refugee board adjudicator erred because she didn't contextualize the female migrant's entire case file.

Park said the adjudicator put too much weight on the fact that the migrant's birth certificate had been scanned for two weeks, but still not emailed overseas for authentication.

The judge disagreed that an error had been made.

"With regard to the contention that the board member failed to take into account the overall context of the applicant's file, it is without merit," he said, adding the adjudicator based her decision on what little information she was provided by government officials.

De Montigny said the arrival of 492 migrants has definitely stretched the resources of the ministry and Canada Border Services Agency, but when the freedom of individuals is at stake, "administrative constraints cannot be a determinative factor."

A decision on exactly when the women will be released will be made by the Canada Border Services Agency. The agency did not immediately return a call for comment Friday.

Nine MV Sun Sea migrants have been ordered released by the refugee board in all.

In the first case, involving a pregnant woman, Ottawa did not request a stay of the release order. It has gone to the Federal Court for such a stay in the other eight cases.

Federal Court hearings in some of the other cases continued Friday.

Last year, when 76 Tamils arrived aboard the MV Ocean Lady, the federal government launched similar challenges when the refugee board ordered them released.