It's a matter of principle.

Meaning

The issue involves a fundamental belief or value.

Examples

• John: I can't compromise on this.
• Alice: Why not? What's the issue?
• John: <b>It's a matter of principle</b>. I won't accept anything less than ethical conduct.
• Alice: I understand. Sometimes, sticking to your guns and stating that '<b>It's a matter of principle</b>' is the only way.