NEW YORK -- Any mounting optimism from four straight days of labor talks between the NHL and NHLPA seemed to abate as negotiations went sour between the two sides Friday.

Multiple sources told ESPNNewYork.com that Friday's evening session ended with some tense exchanges across the table between some of the players and some owners in attendance, as well as NHL commissioner Gary Bettman.

And although progress was made on revenue sharing and some non-core economic issues, there remains a stark divide on the issues that have polarized the two sides since talks began this summer.

"We thought we were much closer together on a structure of a deal than suggestions were," NHLPA executive director Donald Fehr said. "(The NHL) came back to us and said, 'No, we're very, very far apart on a structure of the deal.' "

Bettman declined to characterize the state of negotiations or any details of Friday's discussions.

The goodwill dissipated by the end of the third session -- one that was devoted to tackling the key economic concepts -- but the sniping did not end there.

After the two sides broke for the evening -- they have yet to determine when they'll meet again -- a report surfaced that the NHL feels its latest proposal was not communicated to the players clearly in an internal memo, an assertion that NHLPA executive director Donald Fehr refuted.

"Understand that their proposal is made in front of players, in the room, who hear it," Fehr said. "Owners can't come to meetings when they want to if they want to hear stuff directly but a player can, at the union's expense, come here for himself and all the rest of it.

"That pretty much speaks for itself, I think."

Fehr briefed his membership via conference call with the executive board and negotiating committee on the day's events, which included three separate meetings on critical dates, players' pensions and the core economic issues vital to brokering a new collective bargaining agreement.

The most contentious issue preventing the two sides from forging common ground remains the "Make Whole" concept to honor existing player contracts.

Multiple sources confirmed to ESPNNewYork.com that the league's offer of $211 million was seen as not even close to what the NHLPA seeks to guarantee existing contracts, believed to be approximately $590 million.

Fehr took issue with several elements of the league's "Make Whole" offer, including the fact that the provision only covers the first two years. A source told ESPN.com's Pierre LeBrun that payments in Years 1 and 2 -- $149 and $62 million, respectively -- with the belief that by Year 3 the players will not need to "Make Whole" further.

Fehr also said the two sides were working on agreed-upon growth rates that the league since has indicated they find to be unlikely.

"If the notion is that they are honoring all the contracts and everybody's going to be paid everything they're supposed to according to the letter of the contracts, it's of course not true and never has been," Fehr said.

A source also told ESPNNewYork.com that the two sides remain far apart on players' rights and contracting issues, a vital element to the union's membership. However, two additional sources told ESPNNewYork.com that the league is ultimately willing to budge on those areas if the union is willing to make concessions.

The union, however, believes their willingness to drop to a 50-50 split of revenue by Year 3 (down from 57 percent last year) is enough of a concession.

It remains unclear when the two sides will meet again, although Bettman maintained the league was available whenever the union wanted to reconvene.

He also said that, although his current plan is to attend Monday's Hall of Fame festivities in Toronto, he could scrap that plan if further talks are warranted.

"Whatever it takes," he said. "We're available."

The owners in attendance were Boston Bruins owner Jeremy Jacobs, Washington Capitals owner Ted Leonsis, Minnesota Wild owner Craig Leipold and Calgary Flames co-owner Murray Edwards.