Rival models already have the knives out for the Sports Illustrated (SI) Swimsuit cover beauty Kate Upton.

There was a frosty atmosphere during a launch event last month in front of Caesars Palace in Las Vegas for this year's issue.

Sources said when the 18 SI models -- including Izabel Goulart, Irina Shayk, Chrissy Teigen, Anne V., Genevieve Morton and Julie Henderson -- lined up for a photo, Upton, standing on one side, was asked to move to the middle of the group by a producer.

At first she was hesitant, but moved after further prompting.

But some of the ladies at the shoot were not pleased at making space. An onlooker said one model rolled her eyes while another mumbled under her breath.

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When Upton asked what she said, the model snapped, "Don't worry about me, honey, cause I'm not worrying about you!"

A rep for Upton did not respond to inquiries about the incident. An SI rep said, "If there were words exchanged, it's news to me. Kate was elegant and a complete force of spirit throughout the launch."