A Republican National Convention spokeswoman gave coronavirus health guidelines as the reason, the Associated Press reports.
Delegates are due to gather in North Carolina to formally renominate President Donald Trump.
The 336 delegates will meet on 24 August in the city of Charlotte.
They will cast proxy votes for some 2,500 official delegates. Mr Trump is the party's sole remaining nominee, and his renomination will officially launch his re-election bid.
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