The MLS and the MLSPU reportedly staked out their positions regarding free agency on Tuesday, with the proposed cap on increasing free agent salaries among the issues putting a potential deal in peril, sources told ESPN FC.

For the past month, the two sides have stood their ground on the main sticking points of a deal, with the union threatening to strike if the new CBA does not contain at least some form of free agency, and MLS against any kind of free agency.

But a source with knowledge of the negotiations told ESPN FC that the current offer on the table from the league provides players who are 28 years or older, and who have been in the league at least eight years but not necessarily with the same team, will "have the right to choose their next market" when their contract runs out or when their option is declined.

The source added that the player's previous team will not be able to make a modified offer of a nominal salary increase to keep the player.

MLS' initial offer for free agency would only have affected one player -- Houston's Brad Davis -- but that stance has widened. Troy Taormina/USA TODAY Sports

Some other additional details have also emerged about the deal. ESPN FC television analyst Taylor Twellman tweeted that the proposal dictates that the most a salary could go up at the end of a contract was 10 percent. Twellman also pointed out that players who enter MLS as teenagers may have to wait over a decade to reach the 28 year threshold.

Think of this: If a 15yr old player signs with @MLS (Eddie Gaven), he would have had to play until he's 28 in @MLS to get "rights". - Taylor Twellman (@TaylorTwellman) March 4, 2015

A second source indicated that the current proposal is for eight years, three years longer than the previous deal, and that there is concern on the union side that with the proposed cap on increasing free agent salaries, MLS will now have less incentive to give raises before a player's contract is up.

This could result in an exodus of players to overseas clubs when those deals expire, assuming there is a market for those players. The source also said that the amount of increase in the salary cap is also becoming more contentious, though no details were provided.