Gellar and Prinze are known for wearing couples' costumes for the holiday. In years past, they've celebrated Halloween as Marty McFly and Doc from Back to the Future and Ducky and Andie from Pretty In Pink.
However, the pair chose not to dress up this year because of guidelines around costumes from the acting union SAG-AFTRA during its strike.
"Normally this is when we would post our Halloween couples photo, but due the ongoing strike, we had to scrap our original costumes," Gellar wrote in the caption of an Instagram post on Tuesday (October 31).
"So, if you are out trick or treating tonight and see a very realistic Sarah Michelle and Freddie costume… it might just be us. See you next year."
Last month, SAG-AFTRA released a series of public statements encouraging its members not to undermine the strike by wearing Halloween costumes inspired by film and TV properties.
Instead, the union encouraged its members to dress up in costumes "inspired by generalised characters and figures (ghost, zombie, spider, etc.)".
SAG-AFTRA subsequently had to clarify that its guidelines were not meant for the children of union members.
"Our number one priority remains getting the studios back to the negotiating table so we can get a fair deal for our members, and finally put our industry back to work," a union statement read.
While fans will have to wait until next year for the couple's costumes, Sarah Michelle Gellar recently reunited with former Buffy co-stars Seth Green and Emma Caulfield to see Ed Sheeran in concert.
Other Buffy cast members have reunited this year for a series of audio dramas from Audible called Slayers: A Buffyverse Story, told from the perspective of James Marsters's vampire character Spike.
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