Further cementing his reputation as an outsider in Democratic politics, Comptroller Peter Franchot urged Gov.Martin O'Malley, legislative leaders and rank-and-file lawmakers Wednesday to voluntarily disclose any political donations they've received from "national gambling interests" since their last campaign finance reports were filed.

In a letter to O'Malley, House Speaker Michael E. Buschand Senate President Thomas V. Mike Miller, Franchot said he would "respectfully encourage" such disclosure as the General Assembly prepares to meet in a special session Thursday to consider an expansion of casino gambling in Maryland.

"This voluntary gesture would send a powerful message to the people we serve that Maryland’s oft-stated commitment to progressive values is matched only by our dedication to transparent government," he wrote. "Regardless of how we may feel about this special session and the topic at hand, it would be a statement of values in which all Marylanders could take pride.'

Franchot is an outspoken opponent of gambling expansion and the special session, which he contends is unnecessary.

In his letter, the comptroller cast doubt on the state's prospects for raising additional revenue from a plan backed by the governor to allow a new casino in Prince George's County and table games at all of the slot machine locations in the state.

"There is little to no evidence that this precipitant action by the General Assembly will have any meaningful effect on the current fiscal challenges facing our state," he wrote.

Raquel Guillory, O'Malley's communications director, dismissed the comptroller's letter out of hand.

"Franchot’s letter is riddled with inaccuracies and is completely hypocritical.  I suggest he actually read the bill," she said.

Franchot is among the Democrats expected to contend for the party's nomination for governor in 2014. In positioning himself for that race, the comptroller has tacked to the right and distanced himself from the other potential candidates on budget issues while remaining aligned with many party liberals on gambling.

Though posed in respectful terms, his challenge to lawmakers is hardly calculated to win friends among Democratic legislators, who are left with the choice of declining or combing through their records on short notice to determine which donations might qualify. Campaign committees are not required to report contributions made since the beginning of this year until the fall.

Joe Shapiro, a spokesman for the comptroller, said  a check of Franchot's campaign records showed that he had received no donations from national gambling interests or from David Cordish, the locally based owner of the Maryland Live Casino at Arundel Mills.

Shapiro said that if any such donations come in going forward, Franchot would disclose them.

A spokeswoman for Miller, who has long has a tense relationship with Franchot, said the Senate president's office would not comment. Busch's office agreed to check his records for any such contributions but has not completed that task as of noon Wednesday.