March 6 (Reuters) - Marathon Partners Equity Management wants spirits company Becle SAB de CV, the world's largest tequila producer, to move its listing from Mexico to the United States or review strategic alternatives, including a possible sale, according to a letter seen by Reuters.

The Mexican company's stock, which has traded on the Bolsa Mexicana de Valores since 2017, is "significantly undervalued" and management should either relist it on another exchange or consider bolder steps, including a sale to a bigger rival, Mario Cibelli, Marathon Partners' managing member, wrote to the board.

The letter, sent last month, was seen by Reuters this week.

Becle is valued at $8.5 billion and roughly 85% of the company is owned by Chief Executive Officer Juan Domingo Beckmann and his sister. The remaining 15% is held by investors including Marathon Partners, which owns 15 million shares, and others including Fidelity and Southeastern Asset Management, regulatory filings show.

The move by Marathon Partners, which calls itself a patient and supportive investor at Becle, is a rare example of shareholder activism in Mexico.

Cibelli said in his letter that he was reiterating his earlier suggestion that Becle - the only major spirits company not listed on a major exchange - relist elsewhere to improve liquidity and allow management to repurchase shares more easily.

If management is not ready to do that, it may be time for bigger steps, Cibelli wrote.

"We believe the most value would likely be created from a strategic merger combination that results in a larger and stronger spirits organization to better compete on the global stage," Cibelli wrote.

A Becle representative did not immediately respond to a request for comment.

Becle's portfolio includes the popular Jose Cuervo tequila brand as well as the Great Jones Whiskey and Boodles Gin brands.

"Most spirits company portfolios are under-indexed to tequila in the U.S., and outside of Becle, there is no other meaningful way for competitors to increase their exposure to this popular spirit," Cibelli wrote.

He also wrote that the company's total return since it listed shares seven years ago has dramatically lagged rivals Davide Campari Milano, Brown-Forman, Pernod Ricard, Diageo and Remy Cointreau. Diageo bought actor George Clooney's high-end tequila brand, Casamigos, in 2017. (Reporting by Svea Herbst-Bayliss in Providence, Rhode Island Editing by Matthew Lewis)