Union vs Non-union Jobs, Same Facility

[Carlitos]

After having traveled a bit during Covid, my wife and I are considering making the move to California.  I've already started the process of having my Multi-state Texas license endorsed.  
 

While browsing through the different open positions at various facilities, I've noticed that some differentiate what seems to be the same position.  For example, one facility has open positions for Staff Nurse ER at rate $XXX per hour and will specify "Union:  NO,” while another Staff Nurse ER position at the same facility will have a rate $YYY and will specify "Union:  YES.”  Besides the difference in pay rates, all else seems to be the same.  
 

Can anyone with experience shed some light on this?