Can I use the same pseudonym (pen name) as another published author if the spelling is different?

Your question poses two different but related aspects of intellectual property. One is trademarks and another is copyright registration. First, let's consider the trademark issue. Trademarks work as source identifiers of goods or services. If you use a pseudonym (i.e., a pen name) with a slight variation of another published book author name, then you may cause a likelihood of confusion. Your competition author need not have a federal trademark registration. Senior common law trademark usage will suffice. Whether there is an actual likelihood of confusion depends on several factors including: Usage of the trademark as part of a name. Public recognition of the author's name with a business such as a book title or series. That author's popularity in the public. If there is "no" public recognition or fame for the published author, then that name is not associated with any individual. What is public recognition or fame is subjective and depends on several factors including: Revenue generated from the sale of the book title; Wide recognition in the news media; Publishing industry recognition; Getting on bestseller list such as New york times bestseller list; Extensive social media mentions, etc. If the published author book is in the same genre as yours, with a similar book title name, and pseudonym, then it is more likely that you are infringing. Next for copyright registration purposes, you may register a book with a pseudonym author name. Your pseudonym author name is associated with the book title or series, year of publication. Copyright recognition is only given to original works of authorship. Your work must be different from the published author's work. You must submit the best edition of your work to the library of congress. The nature of submission depends on whether your work is already published or not. Disclaimer: The response is general in nature and cannot be construed as legal advice. If you would like to have legal advice, then please consult any competent attorney privately to discuss your case and establish a proper attorney-client relationship. I only work through my website at https://affordabletrademarkattorney.com/