The Love Actually star has written the screenplay for a movie version of the lives of 19th century poet John Ruskin, his wife Effie Gray and her affair with painter John Everett Millais.
Writer Eve Pomerance claims the story actually comes from her work The Secret Trials of Effie Gray, a play which Thompson's actor husband Greg Wise is said to have starred in 13 years ago.
Pomerance's lawyer says, "He is Thompson's husband, he assisted in writing the screenplay. Wise was listed as the co-writer (although) his name is no longer on the script, except as a researcher. She (Pomerance) contacted Wise to congratulate him and to ask for a small acknowledgement. His reply was that it was an 'original Emma Thompson screenplay'."
Bosses at Effie Film, the firm behind Thompson's project, want a declaration from a judge stating there are no copyright issues so production can move forward.
A spokesperson says, "Thompson applied her own creative imagination to well-known public domain facts of history and biography."
Another writer, Gregory Murphy, previously accused Thompson of ripping off his play The Countess for Effie.