The 24-year-old shot to fame at the end of last year when Messy became a viral hit.
It spent four weeks at number one and is the second most-streamed song of 2025 so far in the UK.
A statement from her lawyers said: "It is with immense disappointment, especially given recent events, that we have had no choice but to respond to recent writing credit claims from Carter Lang on four Lola Young songs by issuing legal proceedings on her behalf.
"Carter's claims are strongly refuted and we will not allow Lola's reputation and integrity to be called into question - particularly so long after the sessions took place and agreements were put in place.
"Lola has always been authentic in her songwriting process and acknowledges songwriting contributions where appropriate.
"This dispute has been ongoing for several months and we look forward to the truth being established."
Young's representative declined to confirm which four tracks were involved in the dispute.
Lang is one of four producers credited on Messy and also worked with her on a number of other tracks.
He made his name by working with R&B star SZA and is now one of the most in-demand producers and writers in music, collaborating with big names including Post Malone, Justin Bieber, Renee Rapp and Rosé.