In a new report, the World Anti-Doping Agency (WADA) says hundreds of attempts to carry out drug tests on Russian athletes this year have been thwarted.
The report, published on June 15, says that more than 736 tests between February and May were declined or cancelled for a variety of reasons ranging from sample collection or athlete whereabouts.
The report includes examples of the lengths athletes from different sports allegedly went to both avoid tests and fool doping-control officers.
It also says doping-control officers faced intimidation and threats of expulsion from Russia by security services and that packages containing samples have been tampered with by customs services.
The report comes two days before track and field's international governing body decides if Russian athletes will be banned from the Rio Olympics in August.
In November, Russian athletes were banned after a WADA report highlighted widespread failing in testing.