Supporters of Maryland gubernatorial hopeful Douglas F. Gansler filed a lawsuit Thursday seeking to prevent the running mate of chief rival Anthony G. Brown, from raising money during the legislative session that starts next month.

The State Board of Elections ruled last week that Howard County Executive Ken Ulman (D), Brown’s lieutenant governor candidate, could solicit campaign donations during the 90-day session even though Brown (D) cannot do so under Maryland law.

The law prohibits statewide officeholders — including Gansler (D), the state’s attorney general, and Brown, its lieutenant governor — from collecting campaign donations during the session. Members of the state legislature also may not raise money, which means that Gansler’s running mate, Del. Jolene Ivey (D-Prince George’s), is subject to the ban as well.

As county executive, Ulman does not hold a statewide office. But the lawsuit filed Thursday contends that he is forbidden to raise money because he is acting “in coordination” with Brown and, therefore, is also covered by the ban.

“The two positions are one team, inseparable, coordinated and working together by law and by their filing,” the suit says. “The two positions do not require separate votes to be cast at the ballot box, and in fact there is only one button to push, one lever to pull or one box to mark.”

The issue has become the latest flash point in a fierce Democratic primary.

The suit was filed by Daniel M. Clements, a politically connected Maryland lawyer who is supporting Gansler, on behalf of two registered voters, who Clements said in an interview are also Gansler supporters.

Gansler has been told about the lawsuit, but Clements said he is not acting at the campaign’s behest.

The arguments in the suit, which asks for an expedited hearing before the start of the Jan. 8 legislative session, echo those made last week by Gansler, who said that “accepting money from powerful special interests during the legislative session is not only illegal, it is unethical.”

Justin Schall, Brown’s campaign manager, declined to comment on the lawsuit Thursday. Last week, he said Ulman plans to carefully follow the guidance given by the election board.

The fundraising ban, enacted in 1997, is intended to limit the ability of moneyed interests to influence legislation.

In a letter distributed to candidates last week, the election board said that even though voters elect the governor and lieutenant governor together, “Maryland campaign finance law clearly considers them separate candidates.”

“Each must pay a filing fee to run for office, and each must clearly establish his or her own candidate committee as a prerequisite to filing a certificate of candidacy,” the board said.

Therefore, the memo concluded, a running mate of a candidate covered by the ban may raise money during the session if he or she is not subject to the ban.

Schall has said that during the session, Ulman intends to put money that he raises into an account separate from the one maintained by Brown.

The election board’s ruling applies not only to the Brown-Ulman ticket but also to others in the 2014 election for governor. On the Republican side, Harford County Executive David R. Craig has picked as his running mate Del. Jeannie Haddaway-Riccio (Talbot). Although Craig is not explicitly covered by the ban on raising money during the session, Haddaway-Riccio is.

The suit filed by Clements in Anne Arundel County Circuit Court names Brown, Ulman and State Elections Administrator Linda H. Lamone as defendants. Lamone could not be reached to comment Thursday.

Usually, lawyers from the attorney general’s office review guidance letters distributed by the election board. Earlier this month, Gansler announced that his office would not be involved in this issue, given that it directly affects his race for governor.

Gansler offered the election board the names of four private lawyers to consult for guidance instead.

Jared DeMarinis, the director of the board’s candidacy and campaign finance division, said last week that none of the four lawyers was available. The board instead consulted the Maryland state prosecutor, whose jurisdiction includes election law violations, DeMarinis said.

State Prosecutor Emmet C. Davitt said last week that his office had reviewed the memo but did not offer legal guidance on the section involving fundraising during the session by members of the same gubernatorial ticket.

The issue has taken on urgency this year because the state’s primaries are being held in June, rather than in September.

When the primary was later in the year, candidates for governor typically did not formally name a running mate until after the legislative session.

Bob Wheelock, Gansler’s campaign spokesman, said Thursday that the Brown-Ulman campaign “is making a concerted effort to keep the pipeline of special-interest money flowing,” adding: “That is a symbolic difference between their campaign and ours.”

Gansler’s office typically would represent the election board in a lawsuit. But a spokesman for the office said Thursday that the board would be allowed to obtain an outside lawyer “because the matter could be seen as directly affecting the attorney general.”

Members of the state election board are appointed by the governor. Lamone reports to the board. Gov. Martin O’Malley (D) is supporting Brown as his successor.

A third Democratic candidate, Del. Heather R. Mizeur (Montgomery), is not subject to the ban on fundraising during session. She is exempted under Maryland law because she is participating in the state’s public financing system.