Pop star Meghan Trainor has said it is "so wrong" that her face has been used in an anti-gay marriage campaign in Australia without her consent.
Australia is set to hold a non-binding postal vote on whether same-sex marriage should be made legal.
The ad, on a Facebook page, featured her image and lyrics from her 2016 song No, urging people to vote against it.
Trainor, a vocal supporter of gay marriage, was alerted to the poster by a fan.
The American singer condemned the ad's message and stressed her support for marriage equality.
I SUPPORT MARRIAGE EQUALITY!Someone in Australia is illegally using my picture for a campaign against marriage equality. So wrong. Not okay— Meghan Trainor (@Meghan_Trainor) August 23, 2017
I've said it before, Everyone should be able to love who they want. I support equality, period. 💖👬👭💖— Meghan Trainor (@Meghan_Trainor) August 23, 2017
The administrators of a Facebook page that shared the image have since taken it down and issued an apology, saying it was sent in by a contributor and they had not recognised Trainor in the image.
When asked by a newspaper in 2015, Trainor said if she could pass any law she wanted she "would pass gay marriage everywhere. Everyone should be able to love who they want".
The issue of legalising same-sex marriage has dominated the Australian political scene over the past month, with both sides lobbying hard.
One of the country's most high-profile business leaders, Qantas chief executive Alan Joyce, reiterated his support this week, saying he would be campaigning strongly for a "Yes" vote.
Hollywood stars including Chris Hemsworth, Miley Cyrus and Margot Robbie have also pledged their support for same-sex marriage.
The $A122m (£74m; $96m) postal vote has been criticised for being expensive and a waste of resources, as government MPs will not be bound to vote in line with the public when it comes to legislating any changes.
The mail method of voting has also been criticised for potentially alienating younger voters, sparking a concerted "get the vote out" campaign from same-sex marriage lobby over the past few weeks.
On Friday, the Australian Electoral Commission revealed that more than 90,000 new voters had enrolled in the past fortnight.
The commission says it has processed more than 765,000 enrolment transactions since the announcement of the vote.
More than 16 million Australians will be able to vote. The first survey forms will be sent out from 12 September and are to be returned by 27 October. The results are due to be announced on 15 November.