Khawaja had the messages "Freedom is a human right" and "All lives are equal" on his boots in the colours of the Palestinian flag during training before the opening Test of the three-match series last week, which the hosts won by 360 runs in Perth.
The Pakistan-born opener intended to wear the boots in the game, according to Australian media reports, but was unable to do so under ICC regulations that prohibit messages related to political, religious or racial activities or causes.
He instead wore a black armband and the ICC said he was in breach its Clothing and Equipment Regulations.
View this post on Instagram A post shared by Usman Khawaja (@usman_khawajy)
"Usman displayed a personal message (armband) during the first Test match against Pakistan without seeking the prior approval of Cricket Australia and the ICC to display it, as required in the regulations for personal messages," an ICC spokesperson said.
"This is a breach under the category of an 'other breach' and the sanction for a first offence is a reprimand."
Khawaja, who scored 41 and 90 in the first Test, had said he believes the statements on his shoes in support of the people of Gaza were not political and vowed to fight the ICC.
In a video on social media, he said: "What I've written on my shoes is not political. I'm not taking sides.
"Human life to me is equal. One Jewish life is equal to one Muslim life is equal to one Hindu life and so on. I'm just speaking up for those who don't have a voice."
"The ICC have told me I can't wear my shoes on the field because they feel it's a political statement under their guidelines. I don't believe it's so. It's a humanitarian appeal. I will respect their view and decision. But I will fight it and seek to gain approval."
England allrounder Moeen Ali, who like Khawaja is a Muslim with Pakistani heritage, was banned by the ICC in 2014 from wearing wristbands featuring the slogans "Save Gaza" and "Free Palestine".
But the ICC did allow players to "take the knee" before international matches in support of the "Black Lives Matter" movement in 2020 and 2021.
Khawaja's response to the reprimand will be the focus of much interest when he's set to take the field in the second Test which begins at the Melbourne Cricket Ground on December 26.
