Bloggers and rights groups have complained that Siri failed to flag up nearby abortion clinics, and in some cases it suggested pregnancy advice centres instead.
However, Apple has been quick to stress that the lack of abortion advice was "not intentional", claiming that it was down to a software glitch.
In a statement issued yesterday to The New York Times, Apple spokeswoman Natalie Kerris said: "Our customers want to use Siri to find out all types of information, and while it can find a lot, it doesn't always find what you want.
"These are not intentional omissions meant to offend anyone, it simply means that as we bring Siri from beta to a final product, we find places where we can do better and we will in the coming weeks."
Siri was a major selling point of the iPhone 4S, allowing users to set reminders, access information and manage their schedules just with their voice. In America, the system answers questions about local services, but this is not available in the UK.
Some groups have expressed concern that the system is seemingly unable to provide certain pieces of crucial information, while others have claimed that a search for abortion clinics directs them to pregnancy crisis centres - critics claim that these centres are set up to counsel women against having abortions.
The American Civil Liberties Union observed yesterday in a blog posting: "Although it isn't clear that Apple is intentionally trying to promote an anti-choice agenda, it is distressing that Siri can point you to Viagra, but not the Pill, or help you find an escort, but not an abortion clinic."
Nancy Keenan, president of NARAL Pro-Choice America Foundation, wrote in a letter to Apple's chief executive Tim Cook that it was "disappointing" to hear that Siri was not providing information on key health issues such as abortion and contraception.
She added: "Although Siri is not the principal resource for women's health care, I hope you agree that it is important that the women who are using this application not be misled about their pregnancy-related options."
Norman Winarsky, who co-founded the Siri technology before it was sold to Apple last year, speculated that the problem could have occurred because the system uses third-part information sources.
"Those answers would be coming from the web services that Siri is connecting to, not necessarily Apple," he said.
"My guess at what's happening here is that Apple has made deals with Web services that provide local business information, and Apple probably hasn't paid much attention to all the results that come up."
But Winarsky said that he had no knowledge of how Siri was adapted after it was acquired by Apple.
This is not the first controversy to hit Siri since its launch, as a security flaw was uncovered in October that meant the system would allow a user's phone to be accessed by someone else even when it was locked.
> Siri co-founder Dag Kittlaus leaves Apple