many factories may have to close down.

Many factories may have to close down.
许多工厂也许不得不（自行）关闭.【强调自行关闭】【主动语态】
Many factories may have to be closed down.
许多工厂也许不得不被关闭.【强调外来机构等发出关闭的动作,不是厂方自身.】【被动语态】
祝你开心如意!