(CNN) The yellow piece of paper hung in the window of the Cafe 8 1/2 in Honolulu, Hawaii. From a distance, it was barely noticeable among other handwritten signs and notes strewn about the restaurant. But up close, it bore a warning:

"If you voted for Trump, you can not eat here! No Nazis"

The sign has invited a huge backlash online, even though the owner says it has been in the restaurant since the election.

Boycotts and debate

The cafe's Yelp and Facebook pages were inundated with negative reviews calling the proprietors "liberal Nazis" and "beyond hateful." Some suggested a boycott.

"So, Cafe [8 1/2] hates Trump supporters enough to say they are not welcomed. Well, I wouldn't patronize a liberal hypocrite establishment anyways. I'm sure you can kiss a [s***] load of business goodbye," one Yelp reviewer said.

Others compared the sign to businesses denying black patrons service in Jim Crow-era America.

More understanding and tolerance from the #prejuduce #LiberalExtremists at Cafe 8 1/2 in Honolulu #BoycottCafe_81/2

pic.twitter.com/8oBcKqFqHl — The Bad Guy (@Mad_Deuce) December 28, 2016

Some questioned how a business could be allowed to refuse service to Trump voters, but other businesses come under public and legal scrutiny for refusing to serve LGBT customers based on religious beliefs. (The bakery referenced in the tweet below was slammed with a huge fine for refusing to make a wedding cake for a same-sex couple in 2013.)

Honolulu's Café 8 ½

THIS IS GETTING TOTALLY OUTTA HAND NOW!

HERE IS THE UPDATE YA'LL!! pic.twitter.com/x7TkFqPotU — ~Deplorable Wurm~2.0 (@JurmDaWurm) December 28, 2016

The cafe's Yelp page is currently "being monitored by Yelp's support team," which often happens when businesses get media attention, and subsequently, waves of emotionally-charged reviews.

There were also those who supported the cafe despite -- or perhaps even because of -- the sign.

"Tried out this cool place," someone posted along with a pic . "I hear it comes highly recommended amongst some circles."

The cafe's owner speaks

"If somebody came in and said, 'Hey, I know you can't tell who I voted for, but I voted for Trump, would you let me eat?' I would say, 'Sure, if you're nice with me and I'm nice with you and you like my food, sit down, no problem,'" he said.

Even though he didn't think much of the sign, he still said he should be able to stand by its message.

"This is my place and if I don't want to serve a Trump person, I can do that," he added.

He said business has been good since the sign went viral, but he took it down on Wednesday.