(Reuters) - Major League Soccer teams began reporting for pre-season training on Friday with the players' union warning that it and the league were "extremely far apart" on talks over a new collective bargaining agreement (CBA).

The league and the players union (MLSPA) have been discussing a new CBA with the current five-year deal running out at the end of January and MLS's 20th season due to start on March 6.

If no deal is struck in time, that would raise the prospect of a lockout or a strike -- a possibility mentioned by Toronto and U.S. national team midfielder Michael Bradley this week.

MLS deputy commissioner Mark Abbott, however, says the process is still in its early stages.

"It is premature at this stage of the discussions to speculate about the possibility of a work stoppage," he told reporters.

"Although there are a number of issues that still need to be resolved, that is true of every CBA negotiation and we are committed to continued negotiations".

While CBA talks are always tough and frequently go down to the wire, the current negotiations have a clear potential sticking point, given that the players are demanding the introduction of free agency.

FREE AGENCY RIGHTS

MLS players do not enjoy the same free agency rights as most players internationally, or athletes in North America's other professional sports leagues.

"The players have made it very clear to the league that they can't continue to play under the current system. At this point, we are extremely far apart on the most important issues," union executive director Bob Foose told Reuters.

"We will continue to work at it but it is difficult to see the path to an agreement from where we are right now.

"What we are talking about with free agency is a right that is enjoyed by every other professional soccer player in the world."

MLS has argued for years that, as a growing new league, it needs to keep a close eye on costs while avoiding bidding wars for players -- both domestically and internationally.

"Our structure has provided the foundation for the growth of our league that we have seen to date and the growth that we expect in the future," said Abbott.

Foose argues that free agency would not harm the league.

"At its most basic level, it is about competition and from our perspective competition leads to improvement and that applies to the league and the teams as much as it does to players," he said.

The union also wants to see a raise in the salary cap, currently set at $3.1 million per team, before considerations of the three slots for designated players on extra deals.

"I think we all agree, I think the league would agree, that more money is going to have to be spent to get better," Foose said.

"That said, we are aware of the investment the owners have made and our proposals are intentionally designed to be realistic and to be things that would grow the league."