"The map is patently unfair," said Del. Neil C. Parrott, a Frederick County Republican who founded MDPetitions, the group that successfully petitioned Maryland's "Dream Act" to referendum.
The new map of congressional districts will be used in next week's state primary and in November's general election. But if MDPetitions succeeds in getting the map on the ballot — and in persuading a majority of voters to reject it — the governor and the General Assembly would have to create a new map for subsequent elections.
The map has angered Republicans, who see it as gerrymandering by Democrats, as well as some minorities, who say it unfairly separates communities to support white incumbents.
Parrott was joined at an Annapolis news conference by two Democrats who oppose the map — Dels. Tiffany T. Alston of Prince George's County and Ana Sol Gutierrez of Montgomery County.
"If you are concerned about this map, this is the only avenue left open to the people," said Alston, referring to the referendum process.
The map, drawn by a commission appointed by Gov. Martin O'Malley, adds a swath of left-leaning Montgomery County to the 6th Congressional District, turning a solidly Republican district into one of the few House seats in the country that Democrats might pick up this year.
It also moves Montgomery County, which has a large minority population, almost entirely out of the 4th Congressional District, now represented by Rep. Donna Edwards, who is black.
Courts have rejected allegations that the map is unconstitutional, but voters could nonetheless reject it as they can other laws.
Parrott and his allies will have to gather roughly 56,000 signatures by June 30 to trigger a referendum. He released a poll conducted by the conservative Magellan Group showing that 49 percent of those surveyed would sign a petition to repeal the map.
Maryland has not typically petitioned many laws to referendum, but that trend seems to be changing. The 2012 ballot already will have a question about the Dream Act, and Maryland's new law allowing same-sex marriage is likely to be put to the voters.
Last year, Parrott created a website, MDPetitions.com, that makes it easier to collect valid signatures. His tool enables petition signers to check their names against the state's list of registered voters, so they know that they are registered and can verify the name they used on the rolls. Small inconsistencies can render a signature invalid.
Parrott's group is also helping collect signatures for opponents of the same-sex marriage law.
Under most circumstances, a law petitioned to referendum is suspended once enough valid signatures are collected. But the map was passed as "emergency legislation" — a designation that means the November election would go forward even if the law is on the ballot.
Should voters reject the district map, the governor and General Assembly would have to redraw it. In 1961, a Maryland redistricting plan was petitioned to referendum by the League of Women Voters. Maryland voters rejected the map in 1962, and it had to be redrawn.
Baltimore Sun researcher Paul McCardell contributed to this article.