(CNN) -- Host countries Poland and Ukraine have been told to take a tough stance on racism during the Euro 2012 soccer tournament by European football's governing body UEFA.
The subject of racism has overshadowed the start of the four-yearly competition, with members of the Dutch squad claiming to have heard monkey chants during an open training session last week.
The Netherlands decided against issuing a formal complaint following the incident in Krakow, Poland, but UEFA has written to the mayors of each host city asking them to adopt a zero-tolerance approach to racist abuse. It also sent a copy to the Polish sports minister Joanna Mucha.
"UEFA has written to the mayors of the Polish and Ukrainian cities where open training sessions are scheduled to take place to ask that all effective and necessary measures -- including an increased police presence -- be implemented to prevent any display of discriminatory or racist behavior at such public sessions," the ruling body said.
"UEFA has also requested that the authorities ensure that any person found to be engaging in racist behavior be immediately ejected from the stadium and its vicinity, and that criminal proceedings be launched against such individuals.
"While to date there has only been one isolated incident, any such behavior is totally incompatible with UEFA's zero-tolerance policy towards any type of discriminatory behavior. UEFA is nevertheless confident that the local authorities will adequately deal with the issue."
The issue of racism has plagued the buildup to the 14th European Championships, with relatives of at least two black England players choosing not to travel to Poland and Ukraine for fear of being abused.
Crowd trouble has also been a problem. Russian officials has called for better behavior from the country's fans following unrest during Friday's opening 4-1 win against Czech Republic.
"We believe that some people who were present at the stadium (behaved) unworthy of the true football fans," read a statement on the Russian Football Union's website. "Those who choose the sports arena for the declaration of his personal political and other positions have no place in the stands.
"The Russian Football Union and the national team of Russia kindly request all the fans of these provocative actions to confront bullies and to cooperate fully with the organizers of the match in matters of security.
"We appeal to all fans who are in Poland. Remember that you represent your country. Respect yourself, your home and your team."
Meanwhile, Germany and Portugal have been charged by UEFA following Saturday's Group B match in Ukraine.
The Germans, who won the match in Lviv 1-0, face action after their fans were seen to throw paper onto the pitch, while the Portuguese have been sanctioned for delaying the start of the second half.
"The UEFA Control and Disciplinary Body will deal with the case on Thursday June 14," the ruling body said.