A former Ottawa fertility doctor used his own sperm to inseminate patients without their knowledge or consent, a family alleges in a new lawsuit that claims DNA tests show he is the father of at least two women whose parents sought help conceiving at his clinic.

A statement of claim filed on Tuesday alleges that Norman Barwin told plaintiffs Daniel and Davina Dixon he used Mr. Dixon's sperm during fertility treatments the couple had at the Broadview Fertility Clinic in the late 1980s, but they now believe Mr. Barwin is the biological father of their daughter, Rebecca, who is also a plaintiff.

The lawsuit says a DNA test confirmed last week that Rebecca is a half-sibling on the paternal side to a woman who was also conceived at the clinic.

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Related: Sperm donor mix-up: Where do these two girls come from?

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Lawyers from Nelligan O'Brien Payne LLP are seeking to have the suit certified as a class action and are asking that Mr. Barwin be ordered to provide a sample of his DNA so other children conceived at his clinic can find out if they are his offspring.

"Dr. Barwin knowingly, recklessly and/or carelessly misrepresented, by his words and actions, the paternity of all members of Rebecca's Plaintiff class to the Plaintiffs and the members of their Plaintiff classes when he knew or ought to have known that Rebecca and the members of her Plaintiff class were not of the biological material selected by their parents at the time of their conception," the statement of claim alleges.

"Furthermore, Dr. Barwin knowingly, recklessly, or carelessly concealed from the Plaintiffs and the members of their Plaintiff classes the true paternity of Rebecca and the members of her class, including that he may be their biological father."

The allegations have yet to be tested in court. Reached by e-mail, Mr. Barwin's lawyer, Karen Hamway, declined to comment.

Mr. Barwin is not new to controversy. In 2013, he was suspended from practice for two months after admitting at a College of Physicians and Surgeons of Ontario hearing that he mixed up sperm in three cases. Two of those cases were the subject of a lawsuit filed in 2010 that has been resolved. He resigned as a physician in 2014.

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Rebecca Dixon, 26, learned she was not biologically related to her father earlier this year.

She has a darker complexion than her parents and, as a child, was occasionally asked if she was adopted. But her parents assured her she was their biological daughter.

In the spring, she was diagnosed with celiac disease, which tends to run in families. Around the same time, her mother read that two blue-eyed parents could not have a brown-eyed child like Rebecca.

The family decided to investigate further. A test of blood types revealed that the man Ms. Dixon had always known as her father could not be biologically related to her: He was type AB and she was type O-positive.

An April, 2016, paternity test confirmed Mr. Dixon is not Rebecca's biological father, according to the statement of claim.

"I was shocked," Ms. Dixon said in an interview. "Your first reaction is to say it doesn't matter. My parents are the ones who raised me. I'm like them."

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The case began after a Vancouver woman started searching for her biological relatives.

Kat Palmer, 25, learned as a teenager that she was conceived using sperm from a donor. An only child, she hoped to find half-siblings.

Ms. Palmer said in an interview she called Mr. Barwin's office three years ago to ask for information about her donor, including records, but Mr. Barwin told her he had none.

She said she then met Mr. Barwin in person. "He said, 'You're an adult. You've got a career. You have a healthy relationship,'" she recalled. "'Isn't that enough?'"

The statement of claim says Ms. Palmer turned to online genetic testing. She said her parents told her the unnamed sperm donor was of German and Irish descent, but when she entered her DNA into the commercial database Family Tree DNA, it revealed her paternal line was Ashkenazi Jewish. The claim says the database later connected her genetically to a second cousin in New York who turned out to be a relative of Mr. Barwin.

The lawsuit says that in 2015, after that discovery, Ms. Palmer contacted Mr. Barwin again and he arranged a paternity test. According to the statement of claim, he later confirmed in an e-mail to Ms. Palmer that the test revealed he was her biological father.

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In September, Ms. Palmer was introduced to Ms. Dixon, who was conceived in Mr. Barwin's clinic about six months before Ms. Palmer.

A genetic test confirmed Ms. Palmer and Ms. Dixon are half-sisters through their paternal line. If Mr. Barwin is Ms. Palmer's biological father, he must be Ms. Dixon's as well, the court filing says.

The two women attended the same Ottawa specialty arts school, and although they did not know each other, their circle of friends overlapped. They now communicate almost every day, and plan to meet in December.

"Keeping this a big secret makes it seem something to be ashamed of. It isn't," Ms. Dixon says. "It's just a fact about my life."