The Republican Party has always been the business party ever since they inherited that tradition from the Whigs in the mid-1800's.
Capitalism gives the right of investors to acquire corporations to produce goods and supply services with limited liability.
Unions give the right of workers to organize and sell their labor collectively in the same manner that corporations set the prices at which to sell their good and services.
Unions guarantee the right of workers in the same way that corporate capitalism limits the liability of manufacturers to the amount invested.
Unions bind workers together for their own benefit in the same way that corporations bind investors together to make profits from their good and services.
None of this is particularly Marxist.