Baltimore hotels had to post the signs in every room.

Baltimore officials forced businesses across the city to put up human trafficking warning posters — with the wrong hotline number.

Legislation passed in January meant the signs had to be posted in every hotel room in the city along with food service firms and adult entertainment businesses, according to the Baltimore Sun.

It was only when officials started drafting fresh legislation to get them in all the city’s municipal buildings that they spotted the costly error, the outlet said.

Along with a phone number, the signs tell human trafficking victims to text a number, writing, “Text ‘BEFREE’ (233722).”

But that just gets an error message — because the correct number is 233733, the Sun says.

“It was an honest mistake,” City Councilman Kristerfer Burnett, who sponsored the bill, told the paper.

The council is trying to see if it can also acquire the number in the misprint — or at least get it forwarded to the correct one — while also putting up stickers to cover the number on all the posters, Burnett said.

Hotels in Baltimore are furious, however, because they have “spent hundreds of thousands of dollars complying with the legislation,” Frank Boston III, a lobbyist for the Maryland Hotel Lodging Association, told the Sun.

Boston was also panicked for human trafficking victims, saying, “It would be a tragedy for a cry for help to fall on deaf ears.”

Maryland has one of the highest rates of “domestic human trafficking” in the country, the Sun said, citing the National Human Trafficking Hotline.