Major League Soccer's plan to have their reserve team clubs enter the US Open Cup instead of the first teams has been blocked by the US Soccer Federation, the league and federation said on Wednesday.

MLS announced on Friday that their teams would not compete in the 2024 US Open Cup, the league instead sending second-tier development clubs, from the MLS Next Pro league, to the nation's oldest football tournament.

The knockout competition, which dates to 1914, is open to all US clubs and MLS's move was heavily criticised by many fan groups and lower division clubs.

It remains unclear whether MLS clubs will now take part at all in the 2024 edition.

MLS Next Pro is mainly made up of MLS reserve teams with some independent clubs also involved.

MLS said in a statement on Wednesday that the US Soccer Federation had blocked the move but made no mention of whether first teams would take part.

"U.S. Soccer has...notified MLS that the Federation is not prepared to grant the necessary waiver for MLS NEXT Pro clubs owned by MLS owners to participate in the Open Cup. Independently owned MLS NEXT Pro clubs such as Chattanooga FC and Carolina Core remain eligible for the 2024 Open Cup."

"MLS is committed to finding a viable solution for the 2024 tournament and is working to find a pathway that addresses its goals and concerns," said the league.

US Soccer confirmed the decision in their own statement.

"After thoughtful consideration, we have informed MLS that the U.S. Soccer staff recommendation, which was adopted by the Pro League Taskforce, is that the request be denied." 

"As we move forward, we will continue our review of the Open Cup to ensure it aligns with the U.S. Soccer strategic pillars. We remain committed to addressing the needs and concerns of all of our members, including MLS, and other stakeholders to enhance and improve the U.S. Open Cup," they said.

MLS had said that withdrawing its teams from the Cup, which tends to draw small crowds until the latter stages, would have freed up six mid-week match dates.

The league had also suggested that allowing clubs to field their development teams would have increased opportunities for young players.

The only non-MLS club to win the Cup since the league launched was the Rochester Rhinos in 1999.