"I'm grateful for a couple things today: Martin Luther King Jr & 10 million followers on IG #MLKDay," read the tweet in question, a caption for a picture of the actor driving a convertible on January 18.
He added an index finger and a fist in darker tone.
The post angered some fans, who accused Efron of being "offensive" and "savage" among others, reported Aceshowbiz.
"@ZacEfron This is one of the most
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Someone also suggested that it should have been two separate posts. A harsher poster said Efron should even delete his Instagram account.
The tweet was up for several hours before Efron noticed the backlash and deleted the post the next afternoon.
"I have nothing but the greatest admiration & respect for MLK," the 28-year-old actor tweeted. "My last post was insensitive & I apologize to anyone who I offended. So sorry.