Property manager threatens to break lock if owners dont leave key

We received a letter in the mail from our condo management company stating that fire sprinkler replacement will be commencing in two weeks, for a 3 week period every Mon., Wed. 7 Fri. The letter stated that if we did not make our residence available by leaving a key with a neighbor or by being home, they would break in using a locksmith. Is this legal? Can they break into my condo if I'm unavailable or unwilling to leave a key? Do fire prevention laws in California make this legal?