The spanning tree priority option is part of the decision process in choosing the alternative port when multiple links are established between neighbouring switches.
The spanning tree priority can be modified with the command
spanning-tree port-priority X on the interface. This can be more specific by including the VLAN number too in the example
spanning-tree port-priority vlan Y port-priority X
If an interface has the lowest priority number in a group of links between switches, that interface will be preferred.