Pricing/EventListener/TaxGroupListener.php
public function onPreDelete(ResourceEventInterface $event)
    {
        $taxGroup = $this->getTaxGroupFromEvent($event);

        if ($taxGroup->isDefault()) {
            throw new IllegalOperationException(); // TODO reason message
        }
    }
public function onPreDelete(ResourceEventInterface $event)
    {
        $taxGroup = $this->getTaxGroupFromEvent($event);

        if ($taxGroup->isDefault()) {
            throw new IllegalOperationException(); // TODO reason message
        }
    }
Pre delete event handler.

@param ResourceEventInterface $event

@throws IllegalOperationException