Iditarod mushers have a new rule to contend with during the Iditarod Trail Sled Dog Race this year: Keeping their opinions to themselves.

Rule 53, the "personal conduct policy," states from the date a musher signs up for the 1,000-mile sled dog race until 45 days after the last entrant completes the event, mushers shall "not make public statements or engage in any public conduct injurious to and in reckless disregard of the best interests of the race" or its sponsors.

Penalties include forfeiture of entry fees, involuntary withdrawal, disqualification or prospective disqualification for a period of years. Those who violate it will be sanctioned at the discretion of the executive committee of the race's board of directors.

The rule itself isn't new. The Iditarod Trail Committee Board of Directors approved the rule at a board meeting in April 2015, ahead of race registration in June.

It's unclear why it was enacted. Numerous requests for comment on the change to both race marshal Mark Nordman and Iditarod CEO Stan Hooley were not returned Tuesday.

However, scrutiny of the rule emerged after recent criticism of primary race sponsor Donlin Gold by musher Dan Seavey.

Seavey, a longtime Iditarod trail advocate, wrote a commentary questioning the company's intentions to build near the trail. Andy Baker, a member of the Iditarod Board of Directors, later wrote a rebuttal.

In an interview Tuesday, Seavey said he's not anti-Donlin or anti-gold mining, just pro-Iditarod trail. He said he wrote the piece to illuminate the fact that the public comment period on Donlin's draft Environmental Impact Statement is set to end April 30.

Seavey, 78, who raced in the first Iditarod in 1973 and last raced in 2012, said he wasn't sure what the new Iditarod rule hoped to accomplish. Seavey, who served on the board of directors for nine years, ending 2011, also wasn't sure how the race would enforce it.

"If they think it's going to gag, then there will be more talk of this rule than the gagging of mushers," he said. "... It's not going to gag anybody, really, who's not real timid anyway."

It was unclear whether such rules would create a chilling effect among mushers. Sportsmanship rules already exist in a number of sled dog races, including the Yukon Quest International Sled Dog Race. Jeff King's Denali Doubles race includes a $75 fine for those caught whining.

The Kuskokwim 300 has a provision similar to the Iditarod's, though race organizer and founder Myron Angstman said the rule is intended to govern conduct during the race, not outside of it. He couldn't recall it ever being enforced.

"We never intended for it to be a prohibition about commenting about the Kuskokwim 300 or its sponsors in other forums elsewhere," Angstman said in a phone interview Tuesday. "That's never even occurred to us."

"We recognize that not only mushers, but people in our community and our board, may very well have strong opinions about things that happen in our community, including our controversial sponsors," said Angstman, a Bethel attorney and 1979 Iditarod veteran. "We would never suggest that you couldn't talk about them and to go so far as (the Iditarod rule)."

In an interview Tuesday, King, a four-time champion who's often been outspoken about the race, supported the Iditarod implementing such a rule. He acknowledged that mushers are often a "wild and varied" bunch with many different goals and opinions. The race isn't the time to "grandstand," he said.

"I'm going to let (the Iditarod Trail Committee) direct me in what they feel is in the best interest of the event, and if I don't like it, I won't race. But that is not the case," said King, who is one of 85 mushers signed up to run this year.