NEW YORK -- The memories of a thrilling NBA season might have to last for a while.

There's no telling when basketball will be back.

The NBA locked out its players Friday when its collective bargaining agreement expired, becoming the second pro sports league shut down by labor strife.

The labor deal ended at midnight after players and owners failed to reach a new contract. The two sides remained far apart on just about every major issue, from salaries to the salary cap, revenues to revenue sharing.

The long-expected lockout puts the 2011-12 season in jeopardy and comes as the NFL is trying to end its own work stoppage that began in March.

It is believed to be only the second time that two leagues have been shut down simultaneously by labor problems.

In 1994, the NHL and MLB were idle from October through the end of the year. The NHL locked out its players from October 1994 until mid-January 1995 and reduced the 1994-95 season from 84 games to 48. MLB endured a 232-day strike from August 12, 1994 until April 2, 1995, which led to the cancellation of the entire 1994 postseason and World Series.

The NBA, aware of the easy, inadvertent contact between team personnel and players, have outlined with great detail what is allowed and not allowed during the lockout.

Coaches, general managers and other front-office officials are allowed to follow players on Twitter, for example, but they can't send them a message or re-tweet a player's message, a source told ESPN The Magazine's Ric Bucher.

Scouting prospective NBA talent also isn't allowed, sources told Bucher. For those who have sons playing in AAU summer action, such as Lakers coach Mike Brown and Hawks coach Larry Drew, that means they must leave the arena or gym as soon as their sons' games have concluded and may not watch any other competition.

They also are not allowed to watch practice or any other competition not open to the public. That also goes for watching the U.S. team competing in the University Games. NBA officials are allowed to fly to China to watch the actual games, but they can't fly to Colorado Springs, Colo., to watch the team train.

Teams were told by the NBA front office that any violation will draw a $1 million fine and the possible loss of draft picks, league sources told Bucher. The first warning was issued during the first round of the playoffs, two months before the lockout was implemented.

Commissioner David Stern and the NBA front office say they will not tolerate any violations.

One league source told Bucher the message from the front office is that the punishment might not be limited to a seven-figure fine.

"The league office is digging in," one GM said. "They made it clear to everyone that they're going to crack down hard on any sign of contact with the players and they said they're going to be very vigilant."

In a call with the labor relations committee on Thursday, Stern recommended that the first NBA lockout since the 1998-99 season be imposed.

"We had a great year in terms of the appreciation of our fans for our game. It just wasn't a profitable one for the owners, and it wasn't one that many of the smaller market teams particularly enjoyed or felt included in," Stern said. "The goal here has been to make the league profitable and to have a league where all 30 teams can compete."

Despite a three-hour meeting Thursday and a final proposal from the players -- which NBA leaders said would have raised average player salaries to $7 million in the sixth year of the deal -- the sides could not close the enormous gulf between their positions.

"The problem is that there's such a gap in terms of the numbers, where they are and where we are, and we just can't find any way to bridge that gap," union chief Billy Hunter said.

Hunter said the union made a "moderate" new financial proposal, but it wasn't enough to keep the two sides at the bargaining table.

Hunter said the two sides plan to meet again in the next two to three weeks.

David Stern announced Thursday that the NBA will lock out its players, effective at 12:01 ET on Friday. Neilson Barnard/Getty Images

All league business is officially on hold, starting with the free-agency period that would have opened Friday. The NBA's summer league in Las Vegas already has been canceled, preseason games in Europe were never scheduled, and players might have to decide if they want to risk playing in this summer's Olympic qualifying tournaments without the NBA's help in securing insurance in case of injury.

And teams will be prohibited from having any contact with their players, most of whom won't be paid until a deal is done but insist they'll hang in anyway.

"We're going to stand up for what we have to do, no matter how long it's going to take," Thunder star Kevin Durant told The Associated Press. "No matter how long the lockout's going to take, we're going to stand up. We're not going to give in.

The lockout comes exactly one year after one of the NBA's most anticipated days in recent years, when LeBron James, Dwyane Wade and the rest of the celebrated class of 2010 became free agents.

That free-agency bonanza -- highlighted by the James, Wade, Chris Bosh trio going to Miami -- got the league started on a season where ticket and merchandise sales, ratings and buzz were all up. That weakened the owners' case that the system was broken beyond repair, but it also demonstrated why they wanted changes, with Stern saying owners feel pressured to spend as much as possible to prove their commitment to winning to fans.

The last lockout reduced the 1998-99 season to just a 50-game schedule, the only time the NBA missed games for a work stoppage. Hunter said it's too early to be concerned about that.

"I hope it doesn't come down to that," he said. "Obviously, the clock is now running with regard to whether or not there will or will be a loss of games, and so I'm hoping that over the next month or so that there will be sort of a softening on their side and maybe we have to soften our position as well."