Step 1: Meaning of forfeiture.
If a shareholder fails to pay call money, his shares may be forfeited.
Step 2: Effect.
Forfeited shares reduce the company’s paid-up capital, because the shareholder’s contribution is cancelled.
Step 3: Conclude.
Authorised capital remains unchanged, only paid-up capital decreases.
Final Answer:
\[
\boxed{\text{Paid-up Capital}}
\]