last resort; final measure
The final option when all else has failed; often used in serious or desperate contexts.
As a last resort, I'm also considering quitting the company.
If negotiations break down, litigation will be the final measure.
最終手段 stresses that it is the last option left when all else fails, while 切り札 can be used earlier as a strong advantage, not only as a last resort.
Compound of 最終 (final, last) and 手段 (means, measure).