It is true that the song "Happy Birthday to You" is protected by copyright and cannot be performed in public without obtaining permission from and paying royalties to the publisher. That's why restaurants make up their own silly birthday songs for their staff to sing to patrons -- it's so they don't have to pay royalties. Every time you celebrate someone's birthday at a restaurant or other public place, you are technically committing copyright infringement by singing "Happy Birthday to You" to the birthday girl or boy.
The tune was written by sisters Mildred and Patty Hill in 1893 and copyrighted in 1934 by their sister Jessica. Although the original copyright would have expired in 1991, two intervening Acts of Congress have extended it through at least 2030. The song earns about $2 million per year in royalties and would probably make a lot more if ASCAP (American Society of Composers, Authors and Publishers) had a representative enforcing the copyright at restaurants.