UEFA and players’ union FIFPro want to strengthen a forthcoming worldwide ban to stop third party investors from owning player transfer rights.

FIFA’s phased-in ban on so-called third-party ownership of players, or TPO, comes into force on May 1.

FIFPro and UEFA said Wednesday they have jointly filed a legal action asking the European Commission to outlaw TPO, too.

The complaint counters an earlier protest against the FIFA ban filed to the commission by the leagues in Spain and Portugal, where the investment model is popular.

"Third-party player ownership is a kind of modern slavery, where you see players belonging to investment funds, or other, generally unidentified, corporate entities," UEFA general secretary Gianni Infantino said in a statement.

FIFPro said the complaint, if successful, will "ensure any potential loopholes and windows for circumvention of the new regulations put forth by FIFA are closed."

TPO is already prohibited in some European countries but has been popular with agents and clubs in Latin America, Spain and Portugal. They say it lets clubs sign players who would otherwise be unaffordable.

The leagues’ complaint argues that FIFA’s ban "violates rules protecting competition," and hurts clubs "with fewer economic resources."

Critics say TPO encourages players to be transferred for profit-taking and threatens football’s integrity.

FIFA agreed to ban the practice after a two-year campaign by UEFA.

-