Major League Soccer's return from its coronavirus shutdown could be in jeopardy after negotiations with the players union hit an impasse, US media reported on Monday.

ESPN reported that MLS had set a deadline of 12pm (16:00 GMT) on Tuesday to reach an agreement on a labor deal or else players could be locked out.

The MLS Players Association and the league had agreed terms on a new collective bargaining agreement in February, with the proposed deal running until early 2025.

However the agreement was not formally ratified, and the MLS has reportedly sought to revise certain conditions of the deal in the wake of the coronavirus pandemic.

The MLSPA said on Sunday its members had voted to approve a deal which included a number of concessions, including salary reductions and reduced team and individual bonuses.

"While a difficult vote in incredibly challenging times, it was taken collectively to ensure that players can return to competition as soon as they are safely able to do so," the union said in a statement.

However according to the Washington Post, there are at least two major obstacles to a formal agreement.

The Post said the two sides have been unable to agree on a proposal which gives players a smaller share of revenue from a television deal due to take effect in 2023.

The MLSPA has also objected to the wording of a force majeure clause which would enable owners to impose salary cuts and suspend contracts in the event of another crisis.

According to ESPN, the league would be able to back out of the collective bargaining agreement if five teams in the league were hit by a 25 percent fall in attendance figures.

The 2020 MLS season has been on hiatus since 12 March, when the Covid-19 pandemic erupted and left US sport at a standstill.

MLS has been working on a plan to return from the shutdown with a 26-team tournament staged in Orlando, Florida starting in early July.