Hijack an authority

Use a Higher Power. Infiltrate or impersonate some sort of an authority that can force its access to the premises. Not exactly covert, though.

A child porn raid targeting a specific employee's computer, or a blanket "audit" of all the machines in the facility for software licensing compliance, are just two of the many possibilities. The latter may also allow insertion of malware or listening devices in relative comfort. Other possibilities can involve an immigration raid, workplace safety inspection or other kind of compliance enforcement annoyance, or even just calling in a bomb threat and letting the bomb squad do our dirty work.

The bomb threat may also serve a role if we want to "depopulate" a surveillance camera supervision center for a while.