The regional effort by Maryland and District officials to raise the minimum wage enters a critical phase this week in Montgomery and Prince George’s counties, with uncertainties that could complicate the passage of legislation, including provisions in state law that allow some municipalities to opt out of the wage increase.

Last month, lawmakers from three localities announced a collaborative effort to lift the minimum wage to at least $11.50 an hour by 2016, with future increases indexed to inflation. Maryland law currently requires applicable employers in Montgomery and Prince George’s counties to pay $7.25 an hour, the federal minimum wage. The D.C. minimum is $8.25.

The collaboration is part of a national movement by state and local governments to address widening income inequality. New Jersey, New York and California have approved minimum wage increases this year. San Francisco and Santa Fe, N.M., also have their own minimum wage. Local officials said their concerted action was designed to increase the chances for success across all three jurisdictions.

D.C. Council member Vincent B. Orange (D-At Large), who is leading the District effort along with Council Chairman Phil Mendelson (D), said last week that the bill could be marked up before Thanksgiving. Orange favors an increase to $12.50 an hour, but indicated that in the final version of the bill the amount could drop to $11.50.

Dynamics on the Maryland side may be more complicated. In Prince George’s, the bill is on the County Council agenda for Tuesday, the last scheduled legislative session of 2013. Bills not enacted by then are considered to have failed and must be reintroduced, according to council rules.

All nine council members have signed on to the measure. Last week, its chief sponsor, Council Chair Andrea Harrison (D-Springdale), told her Montgomery counterpart, Council President Nancy Navarro (D-Mid-County), that “she was in good shape and ready to go,” Navarro said.

But Prince George’s County Executive Rushern L. Baker III (D) has said he wants to leave the matter to the Maryland General Assembly and Gov. Martin O’Malley (D) for statewide action next year. Baker is concerned that establishing a county minimum wage would create a competitive disadvantage for a locality that has struggled to attract top retailers.

That trend will be reversed at least in part Friday when Tanger Outlets at National Harbor is scheduled to open, bringing about 80 high-end stores to the county, including Coach and Calvin Klein. County officials said last week that, had the minimum wage bill been pending when Tanger was deciding where to locate, the company might have chosen a site outside of Prince George’s.

One top Prince George’s official, who asked for anonymity because of the sensitivity of the matter, said Six Flags, a major employer of young workers during the summer, has expressed “tremendous concern” about the minimum wage bill. A Six Flags spokesman did not respond to a phone message Friday.

It is not clear whether pressure from Baker or resistance from Six Flags will have an impact on the fate of the legislation. Harrison did not respond to phone messages on Thursday or Friday. Council Vice Chair Obie Patterson (D-Fort Washington) and Council member William A. Campos (D-Hyattsville) did not respond to requests for interviews Friday.

The chief sponsor of Montgomery’s bill, Council member Marc Elrich (D-At Large), expressed confidence that supporters had at least a five-vote majority on the nine-member County Council, especially since County Executive Isiah Leggett (D) signaled his support for taking action ahead of the General Assembly. Leggett also has been working behind the scenes to broaden the bill’s appeal by seeking to lower the increase from $11.50 to possibly $10.75.

Montgomery’s George L. Leventhal (D-At Large), a council member and chairman of the committee scheduled to hold a public hearing on the bill Thursday, said he anticipated just one session — an unusually brisk legislative pace for a potentially far-reaching bill — and that it would likely reach the full council for action on Nov. 26.

Several factors pushed the bill toward passage, including reaction from the business community, which while negative was not as vehement as expected. Council member Nancy Floreen (D-At Large) described it as “muted.” Members were buoyed by data prepared by the University of Maryland showing that only about 6 percent of the county’s workforce would be affected by an $11.50 minimum wage in 2016.

And, with an election year approaching, there was the prospect of a politically unflattering portrait of a council rejecting a minimum wage increase just weeks after voting for a generous pay boost for members who take office after the next election.

But on Friday afternoon, council attorney Robert Drummer circulated a memo explaining to members that state law allows municipalities to exempt themselves from certain chapters of the county code.

The minimum wage legislation, which is filed under the code’s “Human Rights and Civil Liberties” section, would not apply to Barnesville, Chevy Chase Village, Glen Echo, Laytonsville, Poolesville and Takoma Park, according to Drummer, unless they expressly opted in to its provisions. All other cities, including Gaithersburg and Rockville, would be covered by the law unless they specifically opted out.

Prince George’s has 27 municipalities. It was not known which, if any, would be exempt.

Drummer said state law provides an emergency procedure that permits the county to adopt a law that applies in each municipality with six council votes. It would require the council to hold a new public hearing after giving each municipality 30 days’ notice and to make a legislative finding of “a significant adverse impact on public health, safety or welfare” if the minimum wage increase was not adopted.

It was not clear over the weekend whether this would cause some supporters to back away. Leggett said Sunday that although the legal situation poses challenges, they were “not insurmountable.”

“It should not be a justification for not going forward,” he said, adding that a strong showing by the council, in the form of a near unanimous vote, would compel other jurisdictions to act.

“You set a strong direction that others will follow,” he said.

Mike DeBonis contributed to this report.