Per ESPN's Jeff Passan, the league has inquired about different sign-stealing techniques the Astros allegedly used, including "'buzzing,' via the use of Band-Aid-like wearable stickers; furtive earpieces; pitch-picking algorithms; and other potential methods of sign-stealing."
Officials told players who are potentially in violation of MLB rules they will be granted leniency if they are truthful.
MLB has reportedly yet to determine whether the Astros used any of these methods, but officials from other organizations sent accusations about "the extent of the alleged wrongdoing" to Commissioner Rob Manfred's office.
The investigation comes after former Astros and current Oakland Athletics pitcher Mike Fiers accused the Astros of sign-stealing.
According The Athletic's Ken Rosenthal and Evan Drellich, Fiers said Houston had a setup in 2017 that included a center-field camera connected to a television monitor near the Astros' dugout at Minute Maid Park. Staff members and players would reportedly try to figure out the opposing team's signs, and when they believed they knew the answers, they would bang on a trash can.
Last Sunday, Passan reported Kevin Goldstein, a special assistant to Astros general manager Jeff Luhnow, sent emails to team scouts prior to the 2017 postseason asking them to spy on opposing teams' dugouts to obtain information about their signs.
Manfred announced this week that MLB is investigating the Astros over the past three seasons, not just the 2017 World Series-winning team. He noted there should be "firm, serious disciplinary action" if the league finds any wrongdoing.