If you are fortunate enough to negotiate a contract with a theater, be aware of the obligations as well as the protections this contract gives you. It is the standard contract, called an NV Solo, and has evolved over decades of conflict and compromise.
The first thing to know is: Don’t be afraid to ask questions! If you work for a theater you are not free to do anything you want, even when you have no scheduled performance or rehearsal. It only makes sense, since they are paying you every month whether you work or not. So, if your agent gets you a juicy gig in a time that seems free, you still have to get permission from your theater to take vacation time or any other performing engagement.
Vacation is called “Urlaub”, and here’s where knowledge of the rules can be important.
There are two kinds of Urlaub: Wiederrufliches and Unwiederrufliches (German words are long, so let’s break them down into their compound parts-Wieder-ruf-liches, and Un-etc).
The first: can be revoked/called back (“rufen” = to call & “wieder”=again). This happens when your theater needs you for a unschceduled rehearsal or performance.
The second: “Un” is irrevocable (“Un” = Un or Not). The theater has no right to call you back. They can ask and you can come back as a favor, but it is entirely your decision.
These are the rules and it’s important to know them, but it may be even more important to have a good relationship with your administration. Back in the late 90’s my wife was eating lunch in the Dresden Semperoper Kantine between morning and afternoon rehearsals. Camilla Nyland, still in the early stages of her career, sat nearby and the head of the KBB (Herr Wohrat) approached to talk about a guest engagement she had been offered. It was probably good money but not terribly important for career development. He indicated he was inclined to let her out of rehearsals to do it even though the theater was busy with several productions. Camilla thought a bit, the said, “Nein, ich bleibe bei meinem Theater” (“No, I’m sticking with my Theater.”) After that, she never had the slightest problem getting permission for other guest work. Herr Wohrat trusted her and knew she felt a loyalty to her theater and would always take that into account.
On the flip side, I had an Opern Direktor (Head of Opera) who would deliberately schedule rehearsals to sabotage important guest work for singers in his ensemble. Your only relationship with him was under his thumb. Luckily I had good relations with others in the administration which could counteract this so I was allowed to guest at other opera houses. But sometimes this also involved getting up at 4am after a performance to catch a train so I could be sure of getting back for the 10am rehearsal at my current opera house. Either way, be knowledgeable of your employers and willing to accommodate when called upon at the last minute. Your willingness to help an opera house will return in their willingness to help you.