Jul 23, 2010 8:10 AM EST

Major League Baseball implemented random blood testing for human growth hormone in the minor leagues on Thursday.

It marks the first time a professional sports league in the United States has taken the aggressive step against doping.

"The implementation of blood testing in the minor leagues represents a significant step in the detection of the illegal use of human growth hormone," Selig said in a statement. "HGH testing provides an example for all of our drug policies in the future."

Testing will be limited to players with minor-league contracts because they are not members of the players' association, which means blood testing is not subject to collective bargaining.

"Obviously, we make a separate decision with regard to the minor-league program, but the Major League Baseball Players Association has been proactively engaged in conversations with us on the scientific and logistical issues associated with blood testing at the major league level," said Rob Manfred, executive vice president labor relations for Major League Baseball.

Via ESPN