"Your failure to address these issues straight on will motivate this committee to search for legislative remedies," the Republican senator from Arizona told leaders of the sport and its players union.
Nine months later - with baseball still not having acted - McCain issued a second, sterner warning last weekend. This time, according to sports lawyers, marketers and Capitol Hill staff, the senator's coaxing has a better chance of achieving the desired results.
The difference, experts said yesterday, is largely because of momentum and the more urgent nature of McCain's threat, which, unlike before, establishes a deadline - January - for baseball to toughen its drug program.
"They are going to have to heed this warning," Paul Swangard, managing director of the University of Oregon's Warsaw Sports Marketing Center, said yesterday. "You don't want to be on the bad side of somebody like McCain, because he can make it pretty uncomfortable if he wants to."
Yesterday, baseball commissioner Bud Selig, railing against the use of "these horrible substances," said he would accept McCain's intervention on steroid testing if the Major League Baseball Players Association doesn't budge from the current rules.
"I appreciate the support of Senator McCain on this serious issue of ridding Major League Baseball of performance-enhancing substances and I am grateful for his assistance and concern," Selig said in a statement. "If we cannot resolve this issue privately, I gladly will accept whatever help is offered by Senator McCain to achieve our ultimate goal."
Gene Orza, the union's chief operating officer, said that discussions toward an agreement on tougher drug testing had advanced, but there was more work to be done.
"We've had a series of discussions with the clubs, and in many respects they've been fruitful," he said yesterday after the union opened its annual executive board meeting.
He downplayed reports that the sides were close to a deal, saying, "To suggest we have a deal that either is going to be ratified by the executive board this week or is going to be put in place shortly is simply not right."
Orza said discussions will continue, and a management official said owners hoped they would resume next week. Selig wants tougher rules in place by Opening Day.
"I won't say we're a long ways away," Orza said of an agreement. "I don't want to say it's not possible. I just can't guarantee it."
Drug testing's heightened profile in recent days will make it harder for baseball or the players union to duck an issue that goes to the sport's integrity, Swangard and other sports academicians said.
The failures of drug testing have exploded in the news following reports that Jason Giambi told a federal grand jury he had used steroids, and that fellow slugger Barry Bonds said he may have unwittingly used steroids.
The players risk being cast as villains if Selig convinces the public that the union is resistant to change. For years, that perception may not have mattered, said Gary Roberts, director of the sports law program at Tulane University.
"As an ideological matter the union has believed strongly in the privacy rights of their players," Roberts said. "I think the vast majority of the American public does not sympathize with those views, but [union leaders] Don Fehr and Gene Orza don't keep their jobs based on public approval. They represent the players."
But the climate seems to be shifting, Roberts said.
"In a larger sense, even Don's and Gene's deep feelings about privacy rights have got to be tempered to some extent by the notion that the revelations about Bonds and Giambi create a culture where players feel they have to do these drugs in order to shine," Roberts said.
Increasingly, Swangard said, the issue has become about integrity.
"Even though it would be hard to legislate his type of thing [a drug-testing program], this has become a 'Do the right thing' issue. It's about a code of honor and a code of ethics," Swangard said.
In the absence of significant progress, McCain says he will introduce legislation early next year to guarantee that players adhere to a new minimum drug-testing standard.
According to congressional staff, McCain has examined the drug program of the sport's minor leagues, which have a tougher regimen than what major leaguers submit to. But aides said yesterday that the senator believes it is premature to draft specific legislation, and would prefer his threat remain just that - at least for now. "He's waiting for baseball to do its job," an aide said.
McCain and Congress have a variety of tools, including rewriting the drug-testing provisions in baseball's collective bargaining agreement or threatening to revoke the sport's antitrust exemption. The exemption allows the sport to pool resources and behave in other ways that most business enterprises must avoid in an open marketplace.
Congress has often dangled the antitrust exemption in front of baseball to cajole it - including in 2002, when senators threatened to revoke the immunity to head off a potential strike.
Baseball's drug program is part of collective bargaining, which doesn't expire until the end of the 2006 season, but can be rewritten if the sport and the union consent.
The Associated Press contributed to this article.