Billie Jean King says there's a double standard in tennis when it comes to rules applied to women compared to men.

Serena Williams was penalized a game for calling the chair umpire a thief during an extended argument as the U.S. Open women's final.

Watch the controversial decision from the chair empire:

Serena Williams handed controversial game penalty in U.S. Open Final

Williams was given a 3rd code violation in the 2nd set of the U.S. Open Final, resulting in the loss of a game.  Naomi Osaka would go on to with the match in straight sets 6-2, 6-4.

Williams clashed with chair umpire Carlos Ramos, demanding an apology after he initially issued a warning for a code violation in the second set's second game for receiving coaching, which is not allowed during Grand Slam matches.

Serena Williams fined $17K for U.S. Open code violations

Serena Williams has been fined a total of $17,000 US for three code violations during the U.S. Open final. The tournament referee's office docked Williams $10,000 for "verbal abuse" of chair umpire Carlos Ramos, $4,000 for being warned for coaching, and $3,000 for breaking her racket.

Serena Williams, right, talks with referee Brian Earley during the women's final of the U.S. Open tennis tournament against Naomi Osaka, of Japan, on Saturday.

APTOPIX US Open Tennis

Serena Williams believes U.S. Open ump treated her differently than male player

Serena Williams thought she was treated more harshly by the chair umpire in the U.S. Open final than a man would have been.

Serena Williams, left, was cited by chair empire Carlos Ramos for three code violations during her 6-2, 6-4 loss to Naomi Osaka on Saturday.

Naomi Osaka stuns Serena Williams in controversial U.S. Open final

Naomi Osaka became the first Japanese player to win a Grand Slam singles title when she beat Serena Williams 6-2 6-4 in the U.S. Open final on Saturday.

Naomi Osaka, right, defeated Serena Williams 6-2, 6-4 in the women's final of the U.S. Open on Saturday afternoon. 

naomi-osaka

King tweeted, "when a woman is emotional, she's 'hysterical' and she's penalized for it ." King wrote that if a male player had a similar outburst, he'd be called "outspoken" and have no repercussions.

King also tweeted that coaching should be allowed in tennis.

Serena Williams argues with referee Brian Earley during her women's singles finals match against Naomi Osaka on Saturday in the Flushing neighborhood of the Queens borough of New York City.

Billie Jean King: Serena Williams' treatment at U.S. Open proves double standard in tennis

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