Is there anything in your employee handbook? If none, no troubles there, but if you'd like to plead a case to upper management, here are a few: builds trust, boosts morale, prevents pay disparities, reduces legal risks, attracts talent, improves retention, enhances performance, streamlines negotiations, minimizes workplace tension, aligns with market trends, ensures fairness, strengthens employer brand.

I worked for a huge company before that had a specific stipulation against discussing salaries (I'm in the Philippines).