Fans of Major League Soccer's New York City are "outraged" by Frank Lampard's decision to stay with Manchester City until the end of the English season.
Lampard, 36, signed for New York after being released by Chelsea last June but then joined the Premier League champions on a short-term deal.
His stay has now been extended to the summer, meaning Lampard could miss the first three months of the MLS season.
New York fans group the Third Rail said it "publicly denounced" the decision.
In a statement, the independent supporters group added: "Many fans, including our members, decided to support the team, committed to season tickets, and bought merchandise under the impression that Frank Lampard would be playing for New York City Football Club, not Manchester City.
"Many of those fans are rightly outraged by this decision, and we support any course of action they take to voice their discontent over this decision."
MLS franchise New York City are owned jointly by Manchester City and baseball giants the New York Yankees.
The Third Rail added: "We reject out of hand any suggestion that NYCFC is in any way secondary to Manchester City FC, regardless of the source, and are disappointed that City Football Group would give such an appearance."
Lampard has scored six goals in 17 appearances for City this season.
The Premier League ends on 24 May, while the Champions League final takes place on 6 June - Manchester City face Barcelona in the last 16 next month.
New York City admitted they do not know when Lampard will join the club.
"His exact starting date with New York City FC will be confirmed as the EPL and MLS seasons unfold," said the American club.
"All parties remain in ongoing dialogue to create the best outcome for all."
Former Liverpool player and New England Revolution coach Steve Nicol told ESPN the deal sent a negative message about MLS to fans.
"It's a disaster for that new franchise, a disaster for MLS," he said.
But MLS deputy commissioner Mark Abbott believes the move remains a positive one for US soccer.
He said: "Frank Lampard's performance at Manchester City reaffirms that he is one of the world's elite midfielders and we look forward to him joining NYCFC during the 2015 season."