D.C. Mayor Vincent Gray on Monday vetoed a bill that would have begun the process of reforming the city's controversial certified business enterprise program because it "falls short of the mark."

"I appreciate that the council's work here was well intentioned," Gray wrote in a letter to D.C. Council Chairman Phil Mendelson. "However, it is critical that we get reform of this important program right."

Gray characterized the measure, which lawmakers approved unanimously in December, as "unworkable."

The 28-page bill included an array of changes to the CBE program, including a requirement that 50 percent of the value of major contracts go to certified businesses, up from 35 percent.

Gray said that change was "likely impossible to be met."

Gray also took aim at a segment of the bill that would have increased the number of available preference points. Under the proposal, companies could have received additional points for actions like hiring residents from areas with high unemployment and giving preference to ex-inmates.

But Gray said the new system would be difficult to manage and could unwittingly give an advantage to larger companies.

"This provision is ripe for mischief and can lead to fraud," Gray wrote. "Diluting the preference point system potentially undermines the entire CBE program."

The legislation's author, at-large Councilman Vincent Orange, was not immediately available for comment.