When the government uses monetary policy to decrease the quantity of money, then the demand for goods and services decreases. This change in the demand will lead to lower prices, causing firms to produce fewer goods and services—which requires fewer workers. Therefore, lower prices lead to higher unemployment levels in the short run.
The economy faces a trade-off between inflation—an increase in the overall price levels—and unemployment in the short run. In particular, higher inflation rates usually correspond to lower unemployment levels, while lower inflation rates correspond to higher levels of unemployment.