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A 1775 letter up for sale on Tuesday at the New York auction house, Bonhams, should benefit from its timeliness.

That’s because one of the addressees of the letter is Junípero Serra, the Franciscan friar who founded the first nine missions in what’s now California. Serra is being made a saint by Pope Francis during a Wednesday Mass at the National Shrine of the Immaculate Conception in Washington, D.C. He will be the first Hispanic U.S. saint.

The letter, written by a Franciscan administrator in Mexico City, lays out a new code of conduct for the missionaries, and it required the signatures of all five mission heads at the time, which included Serra.

The auction house’s published estimate is between $60,000 to $90,000, but it isn’t hard to imagine that Serra’s sainthood may bump up the letter’s auction value.

“We certainly hope so,” Catherine Williamson, director of books and manuscripts at Bonhams, told Fox News Latino. “In terms of postal history, it’s such a neat piece.”

The letter boils down to being a sternly worded slap on the wrist for Serra – whose canonization is opposed by Native American groups which claim that he forcibly converted their ancestors and tried to eliminate their cultures – and the other missionaries.

“Ministers may not carry weapons while traveling,” the Spanish letter reads. “Ministers will be cautious in their relations with soldiers.” It adds that they are “forbidden to report anything concerning the missions, Indians or soldiers” to local authorities.

Each head was expected to sign the letter, indicating each one’s agreement to abide by the rules laid out within, then sent on to the next mission. Serra, who was at the Monterey mission at the time, was the second to last person to sign it.

“A lot of it is fairly bureaucratic stuff,” Williamson said. “But there is one note about the baptizing of Native Americans. It says that they should be confirmed and go through a proper catechism course instead doing these blanket baptisms.”

Steven W. Hackel , the author of “Junípero Serra: California’s Founding Father,” told the Wall Street Journal that many of the things the missionaries are being told not to do are things Serra did. “What the letter does is try and rein in Serra’s authority and limit who he can contact directly.”

In a separate letter, Serra said that the rebuke from Mexico City had made him feel “ashamed,” Hackel noted.

Williamson is less sure that the letter targeted him directly. “It’s like getting a memo from the boss saying, ‘You guys are messing up, and here’s how we’re going to fix it.’ He probably did some of the things mentioned, but he wasn’t the only audience.”

In 2008, Bonhams sold a letter written by Serra instructing others in great detail how to establish the mission at San Juan Capistrano.

“Serra was saying, ‘This is what’s going to happen; it’s going to include so many soldiers, so many priests. You’re going to plant this many acres,” Williamson said. According to the Journal, the 2008 letter sold for $372,000.