MLS is notably different from most leagues in the world in that player contracts are owned by the league and not individual clubs and there is no internal transfer market.
The players' union, MLSPU, has a collective bargaining agreement (CBA) with the league that ends on January 31 and the parties have spent the last year in negotiations.
If a new agreement is not reached the league risks being without any contractual arrangements in February, around six weeks before the start of the new season.
"It is certainly our sincere hope that we can have an agreement in place by (January 31)," union executive director Bob Foose told Reuters on Wednesday.
"But in order to do that there are going to have to be significant changes made to the way the league functions and obviously we would have to come to agreement on economic pieces."
MLS commissioner Don Garber warned recently that talk of a strike or shutout was premature and could be damaging to the league and Foose agreed it was too early to be considering industrial action.
"It is certainly not something we have raised at the bargaining table," Foose said.
"There is an old labour (movement) saying that you have to hope for peace but prepare for war and there is certainly some truth in that.
"In any collective bargaining negotiations there is that risk but it is early to be talking about that and we sincerely hope it doesn't come to that."
DISCREPANCIES
This week FIFPro, the international players association representing professionals from 42 nations, urged soccer's global governing body FIFA to tackle what it sees as discrepancies between its statutes and the operating rules of MLS.
"[MLS] ignores FIFA rules in several respects," FIFPro said in a statement.
"There are players without a guaranteed contract, player contracts are routinely terminated by the league, MLS acts as a cartel, there is no freedom of movement for any MLS player and virtually any player can be transferred to another club in the league without his consent.
"[We] demand that FIFA take responsibility in these matters, take account of the views of the players and ensure that the (FIFA) regulations are enforced on a global basis, particularly in the USA".
Garber said last week the union was wrong to say they were not in line with FIFA's rules.
"I will say emphatically that we are operating in compliance with the FIFA regulations and the union is simply wrong on this point," he said.
"We spent a lot of time creating the structure for MLS with tremendous legal support and financial commitment, they have reviewed the regulations and we are in fact abiding by them."
FIFA said in a statement they would not interfere.
Speaking to reporters at the MLS Cup final on Sunday, Garber said talks had been productive but were also tough.
"We understand and accept the fact that they will be tough negotiations but we are very committed to p
