Once a union has gained bargaining rights, they can negotiate a contract which says that a new employee must join the union within a certain time period, or be a nonmember under "agency shop." If the contract negotiated says dues are deducted from the employee's wages and remitted to the union, that is because the union has negotiated certain benefits and wages and if employees were not to join the union they would be "free riders." Private business owners can hire whomever they want. If they want union employees, they can hire them. That's how it works in Nevada, a right-to-work state. An employee doesn't have to be a union member to be hired.