Yes, each employer is given only a set of visas they can use. @acchabaccha is right. They may have applied for a supervisor visa but was approved for a labourer one. Or worst case scenario was they gave you an offer letter as a supervisor but in reality, the visa that they have when they hired you is for labourer designation. Better get it sorted out. There is a huge difference between a supervisor and labourer, more so if it is stamped on your visa. There is a certain stigma concerning the job titles on the visa. Simply put, you will be more credible to anybody here if you have "supervisor" rather than labourer on your card.