(Michael S. Williamson/The Washington Post)

The public won’t know the results of Friday’s vote until the end of June, when the Supreme Court is expected to issue its opinion on the health reform law’s constitutionality. It’s possible, but unlikely, that a justice could change his or her mind between now and then. And if one doesn’t, then Friday’s vote will pretty much secure the future of the Obama administration’s signature legislative accomplishment.

As I reported Thursday, the big vote will happen in Friday’s Supreme Court conference, which only involves the Justices. My colleague Robert Barnes takes us even further inside the wood-paneled room. The meeting reportedly begins with a handshake. Then, the justices take their seats:

The process Friday will begin in the court’s conference room just off the chambers of Chief Justice John G. Roberts Jr. He will take his place at the head of the table, and his eight colleagues will arrange themselves by seniority. No one else will be in the room.

The court’s recent tradition has been that the chief justice lays out the case and then informs the others how he will vote. The process moves from justice to justice by seniority, and the rule is that no one speaks twice until everyone has spoken once.

Junior justices — on this court, Elena Kagan — are often surprised to find themselves casting the deciding vote. (It is also the junior justice’s job to take notes and answer the door if there is a knock.)

Friday’s conference session is not meant to be a place for justices to hash out their thoughts on the health reform law. “There’s not a whole lot of give and take at the conference,” a former Scalia clerk tells the Associated Press’s Mark Sherman. “They say, ‘this is how I’m going to vote’ and give a few sentences.’”

Justices have sometimes changed their minds after a vote, as opinions get drafted and circulated among the nine justices (first drafts will likely be written in about four to six weeks, former clerks tell me). That includes Justice Anthony Kennedy, widely seen as the pivotal swing vote in this case.

In the early-1990s, Kennedy changed his vote in at least two tight cases, flipping the minority opinion to become the majority. One was Planned Parenthood v. Casey, where he ultimately upheld Roe v. Wade’s protection of abortion rights by joining the Court’s liberal wing in a 5-4 majority. The other was a case where Kennedy was supposed to write a majority opinion, for five justices allowing prayer at public school graduations.

“In the end, Kennedy ended up writing the opinion for a different five-justice majority striking down the graduation prayers,” reports AP’s Sherman. “According to several accounts, Kennedy simply changed his mind during the writing process.”

There is one thing, however, that happens even less than a justice changing his mind: Supreme Court leaks. In a city replete with sources slyly passing information off to reporters, the Supreme Court has proved almost immune to having decisions come out before officially issued. A lot of that likely has to do with the very small number of people with access to the information, only the nine Supreme Court justices and their law clerks.

Sherman, however, is able to dig up one case of information leaking early, albeit from three decades ago. “Tim O’Brien, then a reporter for ABC News, informed viewers that the court planned to issue a particular opinion the following day,” he writes. “Chief Justice Warren Burger accused an employee in the printing shop of tipping O’Brien and had the employee transferred to a different job.”

So, beware Supreme Court printing shop employees — your job could be on the line with this one.