"As you will know, I have represented Australia many times and have the proud record of never losing a tennis match while playing for my country. I am disappointed that Qantas has become an active promoter for same-sex marriage. I believe in marriage as a union between a man and a woman as stated in the Bible," Court, 74, said in an open letter published in The Western Australian
CNN attempted to reach Court's church to confirm the letter's validity.
"Your statement leaves me no option but to use other airlines where possible for my extensive (sic) travelling," she wrote.
Alan Joyce, the Qantas CEO, recently had a pie smashed in his face
during a speaking appearance due to his stance over same-sex marraige.
Joyce later said the incident would not stop him from publicly advocating for same-sex marriage, which is currently illegal in Australia.
A plan to put the issue to a national referendum was blocked last year.
Tennis Australia, the governing body for the sport in Australia, said it disagreed with Court in a statement.
"As a legend of the sport, we respect Margaret Court's achievements in tennis and her unmatched playing record. Her personal views are her own, and do not align with Tennis Australia's values of equality, inclusion and diversity," Tennis Australia said.
The first grand slam of the season is the Australia Open, which is held at Melbourne Park with one of its show courts named after the 74-year-old tennis great.
Court's career encompassed both amateur and professional eras in tennis and between 1960 and 1975 she won a record 24 major singles titles, the "best in history, regardless of gender," according to the International Hall of Tennis website
After retiring, she became active in religion and was ordained as a minister.
Billie Jean King and Martina Navratilova -- two other former tennis greats -- are openly gay, but in an interview with The New York Times earlier this year, Court said homosexuality was in many cases "a choice."
"You stand with values for family and different things, so you are a voice, and then you get persecuted for that," Court told the Times.
"You are not hating the people. You love the people, but you get taken that way. And I say marriage is between a man and a woman."