The U.S. Agriculture Department pulled all staff from an annual crop tour on Wednesday.
According to Reuters, the move came after an employee was threatened over the phone by an angry farmer.
Farmers have complained this month that a government crop report did not reflect damage from historic flooding this spring.
They are also frustrated over unsold crops due to the trade war with China, falling farm income and tighter credit conditions.
Sources say police will be present on upcoming stops of the trip, which ends on Thursday.