Williams launched an astonishing verbal attack on chair umpire Carlos Ramos as she crashed to a shock 6-2, 6-4 defeat by Osaka in the women's final.
The 23-time Grand Slam champion was given three code violations by Ramos, the first for receiving coaching, the second for racket abuse and the third for verbal abuse of the umpire.
Williams had demanded an apology from Ramos during her rant and later called the punishment 'sexist', while claiming she was fighting for women's rights because male players got away with similar antics.
While she received widespread support for her actions, Strycova has slammed the 23-time grand slam champion.
'This is a bulls***,' Strycova told Czech website Sport.CZ.
'For umpires being women or men doesn't matter. In comparison, I never saw Nadal shouting like that with an umpire.
'Ramos is tough, one of the best umpires in the world.
'He did what he had to do in that match, because she overstepped the limit.
'Did she have to behave differently only because she was Serena Williams? I find it interesting that she did it only when she was losing.
'Me, as a woman, take a lot of warnings,' she added.
'The WTA defence surprised me. Will rules change in Serena's matches? If it's like this, let me know.'
Ramos has been praised for acting with 'professionalism and integrity' by the International Tennis Federation after the umpire was labelled a liar and a thief by Williams.
'Carlos Ramos is one of the most experienced and respected umpires in tennis. Mr. Ramos' decisions were in accordance with the relevant rules and were re-affirmed by the US Open's decision to fine Serena Williams for the three offences,' an ITF statement said.
'It is understandable that this high profile and regrettable incident should provoke debate.
'At the same time, it is important to remember that Mr. Ramos undertook his duties as an official according to the relevant rule book and acted at all times with professionalism and integrity.'
Williams, who was aiming to equal Margaret Court's record of 24 Grand Slam titles, refused to shake hands with Ramos after the match.
Her $17,000 fine for the code violations, imposed by the United States Tennis Association, will be deducted from the $1.85 million prize she received as the runner-up to Osaka.
Meanwhile, Osaka said Williams's row with the umpire during the US Open final had not altered her feelings about winning a grand slam largely because she had no idea how she was supposed to react.
At Flushing Meadows, the 20-year-old was reduced to tears during the presentation ceremony but on her arrival back in Japan, she said she had not been saddened by the incident.
'For me, I don't feel sad because I wouldn't even know what I'm expected to feel,' she told a news conference.
'Because it was my first final and my first grand slam victory, overall I felt really happy and I know that I accomplished a lot.
'I don't think I even thought about feeling sad because there's no experience for me to draw on (from) any other grand slam final.'