FIFPro said that at some leading clubs in the region, there was a two-tier system where top players were paid punctually and others had to wait.
“There is a big difference between the contracts of the star players and everyone else," Dejan Stefanovic, president of the Slovenian players union SPINS, said in a FIFPro statement.
Stefanovic said lesser-known players sometimes have grace periods written into their contracts, under which they agreed to be paid later.
Slovenia, the homeland of new UEFA president Aleksandar Ceferin, was named alongside Croatia, the Czech Republic and Romania as countries where players were often treated as self-employed.
FIFPro said it had "long championed" the need for standard labour contracts to be compulsory which, it said, was not the case in those countries.
Ceferin, who was president of the Slovenia football federation before being elected UEFA president on Sept. 14, denied in an interview with Reuters before the vote that there was a problem with the way players in his country were treated.
"We have very fair system. Players are satisfied with everything except their salaries," he said, pointing out that Slovenian clubs could never match the wages offered a big clubs in Spain and England.
Serbia’s player union said it has had to contract four additional lawyers because it has so many cases of players chasing up unpaid wages.
"The situation is getting worse,” said the head of the union Mirko Poledica.
Russian clubs, meanwhile, signed players without worrying about whether they could afford their wages, according to Russian union leader Vladimir Leonchenko.
He said that clubs “first sign contracts and then they look for the money.”
European soccer's governing body UEFA has said that it has succeeded in reducing that amount of "overdue payables", including wages, which clubs owe, thanks to stricter licensing regulations.
However, UEFA officials admit it can only enforce those on clubs who qualify for European competition, while the rest depend upon the licensing regulations of their respective domestic leagues.
(Editing by Ed Osmond)
