Senator Bernie Sanders’ Vermont office was evacuated Thursday afternoon after a suspicious package was mailed to the building, authorities said.

Police were alerted to the package at the Democratic presidential hopeful’s Burlington office soon before noon on Thursday and decided to clear the building about four hours later, a local CBS affiliate reported.

Burlington Police announced the evacuation on Twitter Thursday.

“Along with @VTStatePolice, @OneNorthAvenue has responded to a suspicious package at the office of Senator Sanders. Out of an abundance of caution, we have cleared offices in the building while it is assessed,” they wrote.

Authorities investigated and determined it was not a threat before reopening the building.

It’s not clear who sent the package, or why it was deemed suspicious.