Gray is afraid referendum will tick off his buddy Darrell Issa. (Jim Cole/AP)

Mayor Vincent C. Gray didn’t like the idea of using a voter referendum to implement District budget autonomy when it was first proposed, and he still doesn’t like it now that the D.C. Council is poised to make it happen.

Gray (D) sent an eight-page letter to Chairman Phil Mendelson (D) on Monday detailing his objections to the measure, which will have D.C. voters cast ballots April 23 to authorize charter amendments that would give the city greater flexibility in spending money without congressional approval.

“As you know, I fully and passionately support the goal of securing budget autonomy for the District of Columbia as soon as possible,” Gray wrote. “At the same time, I take very seriously my obligation to help ensure that the District Government complies with the governing law.”

Gray said he is “doubtful that Congress has delegated the power to the District to convert unilaterally the role played by Congress and the President in the District’s budget from active participation to passive review.” He added he is “concerned about whether the bill has been carefully enough vetted so as to avoid undermining the District’s crucially important relationship with Congress and our federal partners.”

If passed, he said, “the cause of getting Congress to approve D.C. budget autonomy may be set back many years if Members bristle at this attempt to circumvent their authority. Further, it would be even worse if such short-circuiting hurts our efforts on other significant fiscal and policy matters that the District has before Congress.”

The letter does not mention council testimony from former Rep. Tom Davis (R-Va.), who said he doubted Congress would give a whit about the referendum.

Otherwise, the letter is the closest the Gray administration has come to sharing its legal rationale for opposing the proposal, aside from referencing a confidential memo done by last year by Attorney General Irvin B. Nathan’s office. It goes into some detail about the administration’s concerns about violating provisions in the Home Rule Act and federal antideficiency laws.

The letter also raises several “practical concerns,” including this novel argument:

I am concerned about going down the path proposed by the bill of a charter initiative to accompany the 2013 special election, as opposed to an election that will have a full slate of candidates for the Council and Mayor running as is scheduled in 2014. If, as some have said, the goal of the bill is to send a resounding message to Congress that District residents want budget autonomy, including the referendum during a special election may not be the best approach — turnout for the April 2011 at-large special election was a little above 10%.

The entire council has signed on in support of the referendum authorization bill. It’s expected to pass today without objection.