A US financial regulatory authority has opened an investigation into claims. Apple's credit card offered different credit limits for men and women.
It follows complaints – including from Apple co-founder Steve Wozniak – that threshold-setting algorithms may be naturally directed against women.
The New York Treasury (DFS) has turned to Goldman Sachs, who operates the Apple Card.
Any intentional or unintentional discrimination "violates New York law," said DFS.
The news agency Bloomberg reported on Saturday that technology entrepreneur David Heinemeier Hansson had complained that the Apple Card had given him the 20-fold credit limit of his wife.
In a tweet, Hansson said the difference was that his wife had a better credit rating.
Later, Mr. Wozniak, who founded Apple with Steve Jobs, tweeted that the same thing happened to him and his wife, even though they had no separate bank accounts or separate assets.
Banks and other lenders are increasingly using machine learning to cut costs and promote loan applications.
But Mr. Hansson, creator of the programming tool Ruby on Rails, emphasized how algorithms, not just humans, can discriminate.
US health giant UnitedHealth Group is being investigated for allegations that an algorithm favors white patients over black patients.
Mr. Hansson said in a tweet, "Apple Card is a sexist program, it does not matter what the intentions of individual Apple representatives are, it has a role in which ALGORITHM fully and completely trust them, and what it does is discriminatory "
He said his wife's credit limit was raised as soon as he addressed the problem.
DFS said in a statement that it "will conduct an investigation to determine whether it violated the New York law and ensure that all consumers are treated equally regardless of gender".
"Any algorithm that deliberately or not leads to discriminatory treatment of women or any other protected class violates New York law."
The BBC has asked Goldman Sachs for a comment.
On Saturday, the investment bank told Bloomberg, "Our lending decisions are based on the creditworthiness of a customer and not on factors such as gender, race, age, sexual orientation or other legally prohibited reasons."
Launched in August, the Apple Card is Goldman's first credit card. The Wall Street Investment Bank offers consumers more products through its Marcus Online Bank, including personal loans and savings accounts.
The iPhone maker markets Apple Card on its website as a "novel credit card created by Apple rather than a bank."