Meaning 'in addition' or 'moreover' — used to add something (e.g., この上〜, この上もなく).
彼は仕事ができる。この上、人柄も良いので信頼されている。
He's competent at his job. On top of that, his character is good, so he's trusted.
この上さらに遅刻したら、会議に出られないかもしれない。
If you're any later than this, you might not be able to attend the meeting.
雨で試合が中止になった。この上観客も少なかったら、運営は大変だ。
The match was canceled due to rain. On top of that, if there were few spectators, operations would be difficult.
Used as 'この上は' meaning 'now that things have come to this' or 'since it has come to this, there's no choice but to...'; emphasizes a decisive situation.
この上は計画を変更するしかないだろう。
Now that things are like this, we'll probably have no choice but to change the plan.
約束を破られたこの上は、信頼を取り戻すのは簡単ではない。
Now that the promise has been broken, regaining trust won't be easy.
この上失敗は許されない。全力を尽くそう。
At this point, failure cannot be allowed. Let's do our best.