Would your warehouse workers be able to set their own work days and hours?
Would they be able to subcontract the warehouse work to others at their own discretion, without your prior approval?
Would they be providing their services to other companies in addition to yours, or would they be working for you exclusively?
Would they be trained and expected to do the work according to your business's methods, or would they be free to choose their own ways of doing things?
Would they decide on their own what tools and equipment are needed to do the work, and provide their own tools and equipment?
Would there be an expectation on both sides that the work will be continued indefinitely, or would the work be for a specific project or period of time?
Those are just some of the questions the IRS looks at in deciding whether your workers are employees or independent contractors. IANAL, but I sure wouldn't try to classify warehouse shipping & receiving workers as independent contractors. I wouldn't even need to check with my accountant; I just wouldn't do it.