Park concessionaire Delaware North Co. sent letters and emails this week to nearly 3,000 people who reserved the insulated "Signature" cabins between June and August, warning them that they might have been exposed.
But the cabins hold up to four people, which means that up to 7,000 more visitors could have been exposed.
The park is receiving more than 1,000 calls a day as visitors frightened about a growing outbreak flood phone lines seeking reassurance.
Six people have contracted the virus, and two of whom have died.
Hantavirus can be carried in the urine, saliva and feces of infected deer mice. Humans typically contract the disease by breathing in the rodent feces or urine.
Early symptoms of hantavirus include fever and muscle aches, chills, headaches, nausea, vomiting, diarrhea, abdominal pain and coughing. Health officials advised anyone with those symptoms to seek immediate medical attention.
Yosemite National Park has set up a non-emergency phone line for all questions and concerns related to hantavirus in Yosemite at (209) 372-0822. It will be staffed from 9 a.m. to 5 p.m. daily.
The Associated Press contributed to this report.
