The conciliation service has urged employers to consider allowing staff to work flexibly during the Olympics amid research showing concern about disruption.
A survey of 1,000 smaller firms by printing giant Lexmark showed that over two thirds were worried about travel and other problems, and half did not have a policy on flexible or remote working.
More than one in 10 said they planned to leave the decision until just before the Olympics begin in less than two weeks.
Meanwhile, Acas published new guidance aimed at minimising disruption to business, as well as catering for fans.
Staff could be allowed to watch popular events on TV during agreed times, or be allowed to work flexibly over the Games period, it was suggested.
Firms should ask their staff about their plans for the Olympics and make it clear what the priorities of the business are, said Acas.
The guide added that some workers will get fed up with the "fuss" generated by the sporting event as well as any perceived favouritism to those with sporting interests.
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