Williams hit in the pocket

Serena Williams has been handed the maximum possible fine by US Open officials following her verbal abuse of a line judge in her semi-final with Kim Clijsters.

The grand slam issued a statement from tournament referee Brian Earley having spent the day reviewing defending champion Williams' controversial exit from the tournament at Flushing Meadows.

It explained the American would be fined the maximum permissible on-site fine of 10,000 US dollars for unsportsmanlike conduct.

Williams lost her semi-final with Clijsters on a point penalty having received her second code violation of the match on Saturday night for unsportsmanlike conduct.

The American second seed had picked up her first for racquet abuse after going one set down, and with Clijsters a set and 6-5 up, her temper boiled over when she was foot-faulted at 15-30 on a second serve.

The first violation also earned Williams a 500 US dollar fine, the second seed having earned 350,000 US dollars as a losing semi-finalist.

Williams could be in for further sanctions, possibly a suspension from future grand slams or the loss of her prize money from this year's US Open, as the matter has been passed on for further investigation.

"The Grand Slam Rule Book also allows for an investigation to be conducted by the Grand Slam Committee Administrator to determine if the behaviour of Ms Williams warrants consideration as a major offence for which additional penalties can be imposed," the statement read.

"This investigation has now begun."