Jared DeMarinis, director of the board's candidacy and campaign finance division, told The Washington Post that the case could be sent to the state prosecutor's office, depending on what officials conclude.
Shareese DeLeaver, an Ehrlich spokeswoman, said the letter was only sent to "active donors" and dismissed the concerns as "ridiculous."
"This is the most important letter I have ever written to you," Ehrlich wrote in the letter to contributors mailed this week. "That's why I've taken the extraordinary step of sending you a real dollar bill. . . . I don't expect you to keep this dollar. I'm asking that you return this dollar along with a contribution of $25 or more."
DeLeaver said the campaign used the technique four years ago with no complaints.
"If there's an issue here, it's four years too late," she said.
But DeMarinis said the letter raises "multiple issues."
It is clearly illegal under Maryland law for candidates to give people money to garner their vote. The propriety of what Ehrlich did is less clear, he said.
The law also requires campaign expenditures to be made by check, and this involves cash, DeMarinis said.
The state attorney general's office is assisting with his inquiry, DeMarinis said.
DeLeaver would not say how many dollar bills Ehrlich had put in the mail but said the letter went only to "folks who are most likely to have a proclivity to vote for Bob Ehrlich in the first place."
DeLeaver also rejected the notion that dollar bills could influence election results.
Ehrlich, a Republican who is being challenged for re-election by Baltimore Mayor Martin O'Malley, a Democrat, wrote in the letter that his campaign needs immediate help from donors.
"Time is running out, and my campaign war chest is quickly evaporating as we buy advertising and expand our voter outreach efforts across the state," he wrote.
As of Aug. 25, Ehrlich and his running mate reported having nearly $8.6 million in the bank, compared with the O'Malley ticket's roughly $4.6 million.