The US Olympic swimming trials will allow about 50% capacity for the June competition in Omaha, Nebraska.
A temporary pool will be installed at the CHI Health Center arena, which is to host the trials for the fourth straight time.
The arena near downtown Omaha normally seats about 14,000 for swimming, but that will be cut in half to mitigate the potential spread of the coronavirus.
Since more than 90% of tickets were sold for the trials in their original date in 2020, USA Swimming plans a complete refund. An entirely new sale will begin April 16.
The governing body already took the unprecedented step of dividing the trials into two parts. Lower-ranked swimmers will compete June 4-7.
The top finishers from that group advance to the second part June 13-20, which will feature the country's top-ranked swimmers and leading medal contenders for the Tokyo Games.
USA Swimming split the meet to lessen the number of competitors and support personnel on the main pool desk and practice facilities.