A company continues to make interest payments associated with any loans from a bank, unless the company can continue to operate after the bank repossesses collateral. Perhaps workers could use their own money to make loans, with the company providing collateral consisting of equipment that the workers can seize using the same procedures that a bank would use to seize the same equipment. The important innovation would be giving workers a right of first refusal to make the loan before the company is permitted to get the loan from a bank or from a potential investor in bonds.
Perhaps this seems to be a solution in the absence of any problem. However, if there were deflation as there was during the Great Depression, then unionized workers might experience an effect as though their wages were rising. It's not clear what is the basis for the entitlement to receive what are in effect rising wages while others remain unemployed and legally barred from offering to compete with the unionized workers by working at wages that are constant in real terms. If you have in mind any strategies for reaching the desired conclusion (that unionized workers earned everything they have and are entitled to all of their privileges), then I would like to know what those strategies are. If similar strategies could be used to provide rhetorical support for various dogmas of social darwinism, then it would be interesting to investigate exactly where and how the rhetorical support fails to be sound logical support.
In my proposal, unionized workers would be helping to finance the creation of their own jobs, and would be taking the same kind of risk that banks take, with the associated entitlement to seize collateral if the terms of the loan aren't fulfilled by the debtor.