Serena Williams says the pro tennis ranking system is "biased" against working moms -- and she's living proof -- claiming she took a HUGE hit for taking maternity leave and it's simply not right.
"When I returned to tennis from maternity leave, I was penalized for taking time off: my ranking dropped from #1 in the world to #453," Serena wrote in an op-ed for Fortune.
"That required me to face tougher competition earlier in the French Open, which led to a pectoral injury that forced me to drop out.