Hotels in Kiev, Donetsk, Kharkiv and Lviv, the four Ukrainian host cities, have hiked prices in some cases more than 10-fold.
Talking to reporters during a visit to Lviv, Platini said "bandits and swindlers who want to earn a lot of money" could keep fans away from Ukraine.
"You cannot raise prices from 40 euros to 100 euros to 500 euros from one day to the next," added the president of European football's ruling body. "That is just not done."
Ukrainian President Viktor Yanukovich this month ordered his government to investigate price hikes and ensure hotel rates are at an "economically reasonable" level during the championships.
"We will be preparing to the last night and will welcome [guests and participants] the way it should be done," Yanukovich said in a statement on Thursday.
The cheapest Lviv hotel listed on UEFA's championship website as available for the Germany-Portugal match on June 9 charges 195 euros per night. For the Ukraine-Sweden match on June 11 in Kiev, offers start at 104 euros.
A tent camp set up 35-km away from Kiev plans to charge 30 euros per night.
Ukraine, tournament co-hosts along with Poland, has invested billions of dollars in Euro preparations and hopes to gain a return in the form of increased tourist traffic.
