Which of the following is a barrier to entry that might be faced by a firm?

The barrier to entry that might be faced by a firm from the options provided is **licensing requirements**. Licensing requirements can create obstacles for new firms trying to enter a market, as they may need to obtain specific licenses or permits, which can be costly, time-consuming, or require meeting certain regulatory standards.

The other options do not represent barriers to entry:
- **Shortage** refers to a situation where demand exceeds supply, not a barrier to entering a market.
- **Low input prices** would generally be favorable for new firms rather than a barrier.
- **A high market equilibrium price** might present an opportunity for profits but does not inherently block entry into the market.