I'm port tack on the layline with starboard coming at me — what can I call?

Under Rule 20, if you are approaching an obstruction (including a starboard-tack boat you'd have to keep clear of) and you need to tack to avoid it, you may hail 'Room to tack!'. The hailed boat must either tack as soon as possible, or reply 'You tack' and give you room to tack and avoid her.

<iframe width="560" height="315" src="https://www.youtube.com/embed/JZGkfaFWjZI" title="Sailing Kiwi" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
<p><a href="https://sailing.kiwi.nz/upwind/case-10-room-to-tack-obstruction/">Source: Sailing Kiwi</a></p>