NEW YORK -

Major League Baseball on Monday suspended 13 players, including New York Yankees star Alex Rodriguez, after an investigation into the use of performance-enhancing drugs.

The league suspended Rodriguez for 211 regular-season games through the 2014 season, but the 38-year-old slugger said he planned to appeal. Twelve other players have accepted 50-game suspensions without pay.

A-Rod and the other players are accused of having ties to the now-shuttered Biogenesis anti-aging clinic in south Florida and taking performance-enhancing drugs. Rodriguez has denied the accusation.

"I'm fighting for my life. I have to defend myself. If I don't defend myself, no one else will," he told reporters after the league announced its decision.

The last seven months have been a "nightmare," he said.

It "has been probably the worst time of my life for sure," said Rodriguez, "obviously for the circumstances that are at hand and also dealing with a very tough surgery and a rehab program, and being 38."

Asked directly whether he had used performance-enhancing drugs, he declined -- repeatedly -- to comment.

"I think we'll have a forum to discuss all of that, and we'll talk about it then," Rodriguez said.

Earlier in a written statement, he said that he was disappointed with the penalty and intends to appeal. He thanked family, friends and fans for their support and stressed that he was eager to get back on the field with his teammates.

His suspension is set to go into effect on Thursday, the league said. But officials also said that Rodriguez could keep playing if he appeals.

He arrived Monday in Chicago, where he played in a night game against the White Sox. The Yankees' roster listed him in the starting lineup, batting fourth and playing third base.

At his first at-bat, Rodriguez was met with boos and some cheers from the crowd. He hit a single to left field.

Before the game started, Yankees manager Joe Girardi said Rodriguez's suspension wouldn't affect the team.

"He's here. He's going to play," Girardi told reporters. "It really doesn't change anything for us."

Major League Baseball's sweeping investigation shows a change in how officials handle performance-enhancing drugs, CNN sports reporter Rachel Nichols said.

"It used to be that baseball protected its own," she said. "And now we're seeing other people in the clubhouse, from managers to the players, saying, 'You know what? Go after these guys. We don't want them in the game.'"

On Monday, Commissioner Bud Selig said the league had no choice but to investigate the allegations in order to "maintain integrity, fairness and a level playing field."

"Despite the challenges this situation has created during a great season on the field," he said, "we pursued this matter because it was not only the right thing to do, but the only thing to do."

Sports Illustrated writer Ben Reiter described the suspension of Rodriguez as "unprecedented."

"The sheer magnitude of the suspension is just one we've never seen before," he said.

Union: 'We agree with his decision to fight his suspension'

The league said Rodriguez's punishment is based on his alleged use and possession of banned performance-enhancing substances, including testosterone and human growth hormone, for multiple years.

Officials also accuse him of "engaging in a course of conduct intended to obstruct or frustrate" their investigation into the matter.

The Major League Baseball Players Association said Monday that it's standing behind Rodriguez.

"We agree with his decision to fight his suspension," the union said in a written statement, adding that it believed the league's commissioner "has not acted appropriately."