Martin said Diaz wouldn't allow him to throw new baseballs back to his pitchers after fouls during New York's 6-5 win over the Los Angeles Angels on Wednesday night.
"Laz Diaz is a d---. Write it hard," Martin shouted as he came into the clubhouse.
Martin said the ball ban was put into effect after he and Diaz exchanged some words over strike calls early in the game.
"He said that it was a privilege that I had to earn, for me to throw the ball back," said the catcher, a seven-year veteran and three-time All Star. "That's never happened to me before. I even told him, because there's guys on base, I like to keep my arm loose. Nope. 'I'm not letting you throw the ball back.' That's pretty strange, to me. That's a good story, huh?"
Martin and Diaz got into it early in the game, and Martin said Diaz "was punishing me" by making all the throws himself.
"I think it happened in the second inning or something," Martin said at his locker after the game. "And then even at the end of the game, after I got hit in the neck, I'm like, 'can I throw the ball back now?' He's like still, no. I'm like, 'you're such a d---. You're a d---, dude. Like, for real. Unbelievable.' "
Martin said he had no previous history with Diaz.
"Now, thinking back, I should have shown him the gold Rawlings sign on my glove," said Martin. The stamp is a sign for having won a Gold Glove, as Martin did in 2007.
It will be interesting to see where this mini-feud goes the next time Diaz is working the plate at a Yankees game. Said Martin: "I know he can hold a grudge with the best of them."
Diaz was unavailable for comment because Martin spoke nearly an hour after the game.
A league spokesman on Thursday said Major League Baseball was "looking into" the situation.
The review could be as simple as viewing the video from the game or it could eventually entail interviewing all the parties involved in the incident.
Yankees general manager Brian Cashman said, "Russell exercised his First Amendment Rights."
Cashman said he would talk with Yankees manager Joe Girardi about the situation, but he declined to comment when asked if the team would pursue anything.
"The normal process is if the league has a problem with a team they deal with the team," Cashman said. "If a team has a problem with the league, they deal with the league. That's all."
Information from The Associated Press and ESPNNewYork.com writers Wallace Matthews and Andrew Marchand was used in this report.