A more thorough explanation:

An open-shop–closed-shop operation, also known as a double-breasted operation, is a business arrangement where the owner operates both a unionized business and a non-unionized business that offer similar services. This allows the owner to compete for contracts from both unionized and non-unionized clients.

For example, a construction company may have two separate businesses: one that is unionized and one that is not. The unionized business would bid on contracts that require union labor, while the non-unionized business would bid on contracts that do not require union labor.

Another example is a restaurant owner who operates two restaurants: one that is staffed by unionized workers and one that is not. The unionized restaurant would cater to clients who prefer to support unionized labor, while the non-unionized restaurant would cater to clients who do not have a preference.

These examples illustrate how a double-breasted operation allows a business owner to cater to both unionized and non-unionized clients, which can increase their chances of winning contracts and attracting customers.