Replacement officials have faced increasing scrutiny through the season’s first three weeks. (Jonathan Ernst – Reuters)

Representatives of the NFL and locked-out referees negotiated all day Tuesday and into the early morning Wednesday, and several people familiar with the talks said a deal is possible in the coming days but still far from certain.

[Click here for latest updates: There’s some optimism a deal could be reached by this weekend.]

The negotiations are at a precarious stage, said one person with knowledge of the discussions speaking on the condition of anonymity because of the sensitivity of the topic. The person said an agreement is possible this week but the talks remain in jeopardy of collapsing completely.

However, another person with knowledge of the negotiations said Tuesday night that the owners of the 32 NFL franchises are firmly against making any further compromises in the talks with the referees.

Replacement officials have worked the preseason and the first three weeks of regular season games with the members of the NFL Referees Association locked out by the league.

Criticism of the replacement officials by players and media members has intensified in recent weeks, reaching a fever pitch after the Seattle Seahawks were awarded a controversial winning touchdown catch Monday night to beat the Green Bay Packers.

The NFL announced Tuesday that it backed the replacement officials’ decision to award the catch for simultaneous possession between Seattle wide receiver Golden Tate and a Packers defender. But the league also conceded the officials missed an offensive pass interference penalty on Tate that would have ended the game with the Packers winning.

Tuesday’s bargaining session was scheduled prior to Monday night’s controversy, and some people close to the talks said the furor over the call would have little or no effect on the league’s stance in the negotiations.

Tuesday’s talks began around 8:30 a.m. and lasted beyond midnight. NFL Commissioner Roger Goodell and league attorney Jeff Pash participated in at least portions of the talks.

The two sides have been at odds over salaries, pensions and non-economic issues that include the league’s desire to make some officials full-time employees and improve its ability to get rid of officials that it considers to be under-performing.

The pension issue appears to have emerged as a major sticking point late in the negotiations.