draw the line

draw the line (to stop continuing to do something; to refuse to do something; to set limitations on what you will do) — класть предел, конец; ставить точку; твердо сказать нет; решительно отказаться; (это уж) увольте; от этого увольте

Example 1: "Even though I felt uncomfortable doing it, I had been writing for a prisoner for years. When I found out what he was convicted of, though, that's when I drew the line."

Example 2: "I have completed every honorable task you have set before me, but now you want me to go rob your sister? I have to draw the line here."

Example 3: "I will cook and clean, but taking care of pets is where I draw the line." —... но еще и за домашними животными присматривать — нет, это уж увольте.

Cf:
draw a line (between sth) (to think or show that one thing is different from another) — провести границу, провести различие

Example: Adolescents often use drugs simply to try to draw a line between their own and their parents' way of life.

Comments
— Vivi
Is 'draw the line' compatible with 'pull the plug'?
— Samantha (native speaker)

Not quite. "Pull the plug" does mean to put an end to something, but not in the same was as "to draw the line".

"To draw the line" is really used when someone is setting limitations, or is affirming one's morals, whereas "pull the plug" is usually used simply to stop something, such as the production of something. It's a slight difference, and a bit difficult to explain.

Example: "I want you to pull the plug on all of the tax reports."

You can't say "I want you to draw the line on all of the tax reports."

I'm not sure if I explained that well enough, so let me know if you are still unclear. :)