Mayor Thomas Menino on Thursday rejected a controversial plan to redraw City Council boundaries, pointing to District 4’s high concentration of voters of color as a factor.

“I am returning, with disapproval, your ordinance even though I recognize your efforts,” he wrote in a letter to the City Council. “My central objection is my concern that the plan concentrates our many citizens of color into too few districts, and in doing so may limit their equal opportunity to elect candidates of their choice.”

He added: “The concentration of black voting age population and non-white voting age population in District 4 is of particular concern. Under the map passed, almost 70% of the district’s voting age population is Black and almost 95% is Non-White. In a city where diversity is found broadly, I ask that you endeavor to avoid over-concentration of minority voters.”

District 4 is represented by City Councillor Charles Yancey, and includes parts of Dorchester and Mattapan.

The council, which voted 7-6 in favor of the proposal, has a November deadline to come up with a new map. The council's redistricting committee is headed by District 2 Councillor Bill Linehan.

“It has always been the intention of the Council and the Redistricting Committee to create a map that represents all interests of the city,” City Council President Stephen Murphy said in a statement. “We are encouraged by the spirit of cooperation that the Mayor and his team offered and look forward to moving this issue toward a resolution that works for all.”

A coalition of voting rights groups and civic organizations had threatened to launch a lawsuit if the mayor signed the proposed map.

“I am grateful Mayor Menino vetoed the redistricting map," City Councillor At-Large Felix Arroyo, one of the six who voted against the map, said in a statement. "I voted against the map because I believed we could do better. This is an opportunity to pass a map that best reflects our City and ensures everyone can have a voice in our government.”

City Councillor At-Large Ayanna Pressley, another opponent of the map who, like Arroyo, was down in Charlotte for the Democratic National Convention this week, took to Twitter. "I am glad to hear that Mayor Menino vetoed the redistricting plan," Pressley said. "Back to work."