Short stack All-in, player can call or complete bet?

[arnaldo]

Blinds 1000/2000, Player A goes all-in for 500, can subseuqent players just call the all-in (500) or they must complete the level's  minimum bet of 2000?

[Dave Lamb]

Before the flop:

All players must call the amount of the BB.

After the flop:

Subsequent players may just call the all-in bet of 500.

[Stuart Murray]

Before the flop:

All players must call the amount of the BB.

After the flop:

Subsequent players may just call the all-in bet of 500.