Serena Williams was fined 10,500 dollars on Sunday for her angry outburst at a line judge that ended a US Open semi-final and the incident is being investigated by the Grand Slam Committee.
US Open tournament referee Brian Earley said in a statement on Sunday that Williams has been levied the maximum possible fine for unsportsmanlike conduct, 10,000 dollars, plus a 500-dollar fine for racquet abuse.
Williams, in a statement on Sunday after the fine was announced, issued no apology or comment on the punishment but stated she "let my passion and emotion get the best of me" and "handled the situation poorly".
The fine is a mere pittance, even at maximum strength, since Williams received 375,000-dollar for her semi-final run at Flushing Meadows, her matches among the top drawing cards for ticket buyers and television viewers.
But the probe underway could bring more penalties.
"The Grand Slam Rule Book also allows for an investigation to be conducted by the Grand Slam Committee administrator to determine if the behavoir of Ms Williams warrants consideration as a Major Offence, for which additional penalties can be imposed," Earley said.
"This investigation has now begun."
US Open officials were reviewing videotapes of the confrontation and the bizarre ending to her loss to Belgium's Kim Clijsters. Williams and match umpire Louise Engzell were interviewed by Earley on Saturday night.
US television commentators and former players Pam Shriver and Mary Joe Fernandez called for 11-time Grand Slam champion Williams to apologise for threatening the woman who called a foot fault upon her to give Clijsters two match points.
Williams walked toward the woman who made the call, waving her racquet before her, and launching into a profanity-tinged tirade of threats that led to the unsportsmanlike conduct violation.
Because Williams had already received a warning after smashing her racquet following the last point of the first set, the penalty point she was assessed handed Clijsters a berth in Sunday's final.
"Last night everyone could truly see the passion I have for my job," Williams said in a statement.
"Now that I have had time to gain my composure, I can see that while I don't agree with the unfair line call, in the heat of battle I let my passion and emotion get the better of me and as a result handled the situation poorly.
"I would like to thank my fans and supporters for understanding that I am human and I look forward to continuing the journey, both professionally and personally, with you all as I move forward and grow from this experience."
Fernandez found the statement inadequate.
"It was basically what we knew. But there was no remorse," Fernandez said. "There was no apology. For herself and for the fans, I think she really needs to come out with an apology."
World number one Roger Federer, going for a sixth consecutive US Open's men's crown Monday, called the controversy "unfortunate".
"She probably shouldn't have reacted the way she did, but I don't think it should take anything away from what Kim has achieved," Federer said. "That just leaves sort of a sour taste for everyone, unfortunately."
Williams will return to Arthur Ashe Stadium on Monday afternoon to join her sister Venus in the US Open women's doubles final against top seeds Cara Black of Zimbabwe and American Liezel Huber.
Grand Slam events fall under the purview of the International Tennis Federation, not the ATP and WTA tours, with the four major tournaments collaborating to form the Slam committee.