There’s no law against it, but some employees may feel that announcing their birthday violates their privacy. While it’s great that you want to recognize your employees and celebrate with them, I recommend not announcing an employee’s birthday without first getting their permission.
In the case of announcements on public social media, I would get a signed acknowledgement that the employee has given you permission to share their birthday and that their doing so is completely voluntary. Announcing birthdays on public social media pages is a little riskier because these posts can be seen by everyone.
You could instead make the announcements internally (still with permission). Popular approaches include email, newsletter, or intranet. Many offices have a birthday celebration each month and announce the employees who have birthdays during that month without mention of their exact birthday. This is a way to celebrate employees and increase morale without putting any given employee in the spotlight.
Answer from Kyle, PHR:
Kyle is a professional author, editor, and researcher specializing in workplace culture, retention strategies, and employee engagement. He has previously worked with book publishers, educational institutions, magazines, news and opinion websites, nationally-known business leaders, and non-profit organizations. He has a BA in English, an MA in philosophy, and a PHR certification.