The Hate Disease by Murray Leinster

As it happened, the timing was critical, though Calhoun hadn't realized it. There were moving lights on the highway to the city at the moment Calhoun and the grid operator went into the Med Ship and closed the air-lock door behind them. The lights drew nearer. They raced. Then ground cars came rushing through the gate of the spaceport and flung themselves toward the wholly peaceful little Med Ship where it stood seeming to yearn toward the sky. In seconds they had it ringed about, and armed men were trying to get inside. But Med Ships land on very many planets, with very many degrees of respect for the Interstellar Medical Service. On some worlds there is great integrity displayed by spaceport personnel and visitors. On others there is pilfering, or worse. So Med Ships are not easily broken into.

They spent long minutes fumbling unskillfully at the outer air-lock door. Then they gave it up. Two car loads of men went over to the control building, which now was dark and silent. Its door was not locked. They went in.