French musician Yann Tiersen has threatened legal action against an anti-gay marriage group.

The 41-year-old Tiersen, best known for his scoring of the 2001 film Amelie, is unhappy with the Christian conservative group Transforma Chile's use of his instrumental J'y Suis Jamais Alle (New Found Glory) as background music in a video to promote its march in support of Chile's ban on gay marriage.

“We would like to make it clear that the use of Yann's track J'y Suis Jamais Alle in the video for 'Marcha por los Valores y la Family,' posted by the political group Tranform Chile, is not authorised and the content of the video is not condoned by Yann or anyone working with him,” an August 1 note on Tiersen's official website reads. “We are currently looking into this further and would like to thank everyone who has emailed and messaged to let us know of the misuse.”

Last week's march through the streets of Santiago drew roughly 1,000 people to protest President Sebastian Pinera's plan to recognize the unions of gay and lesbian couples with a legal contract called the Non-Marital Cohabitation Agreement. It's not full marriage, and couples must live together for more than a year before they can enter the union.

Critics claim the union would undermine marriage.