This can quickly get into legal assistance, which would require at least a legal aide society or Law school volunteer assistance, if there is an issue that is affecting you personally. But you can also do quite a bit of research on your own, if you want to read laws or news articles about this. For example, there are state sites such as Maryland Law Library, which links to Maryland laws. You can either browse categories or search, which gets 180 hits for: privacy, and 5 hits for: privacy and library. You can find some local ordinances in city of county sites, but that seems more hit-or-miss. Federal laws can be searched at uscode.house.gov, which gets 3 hits for: "library records" and 180 for: library and records. Other words to try would be: privacy, confidentiality, and maybe even "identity theft", which gets 21 hits. But also, you would probably want to search for POLICIES in your library's website, possibly under administration or staff - IF those pages are publically available. University libraries, especially public ones, may be more likely to have policy documents open to public view - for example, the University of Maryland Libraries' Administrative Memos, which in turn link to University Policy But if the particular library you are dealing with does not seem to have an easily findable policy (not even via its "site search"), you can either go to the next higher level (the county or state page) to see if they have policies linked. If these suggestions don't work out, a reference librarian at your specific library should not object at all about helping you locate such a policy - which could well be different at that library than it is here at a big public university.
As another example, in New Mexico, the Santa Fe Code, has a search function. Administrative Section 2.17 covers the library:
"2-17.3 Librarian and Other Personnel. A qualified head librarian, other librarians, or other personnel necessary for the operation and maintenance of the library shall be regularly employed by the city. (Ord. #1962-13, §8; Code 1973, §15-3; Ord. #1979-34, §15.1-3; Ord. §1980-41, §4; SFCC 1981, §8-1-4) 2-17.4 Duties of Librarian. The duties of the librarian shall be such as are usually imposed on persons in like employment. The head librarian shall be considered the staff liaison to the library board, serve as the board's secretary, and shall have sole charge of the administration of the library under the direction and review of the department head and city manager. The librarian shall be responsible for the direction of the staff, the efficiency of the library service to the public, the operation of the library and the financial condition set forth in the annual budget. The librarian shall attend all library board meetings. (Ord. #1962-13, §9; Code 1973, §15-4; Ord. #1979-34, §15.1-4; Ord. #1980-41, §5; SFCC 1981, §8-1-5)"
New Mexico has a Librarian's Toolkit that includes Library Laws of New Mexico This very long page has many links to plow through, so you can use CTRL-F to find words such as privacy. One of the privacy hits is: 18-9-4 "Release of patron records prohibited."