Support is dwindling for a ballot question that would impose mandatory limits on the maximum number of patients that can be assigned to one nurse, according to a new poll out Wednesday.

Thirty-one percent of likely voters in the WBUR/MassINC poll said they'd vote "yes" on Question 1 if the election were held today, down from 44 percent a month ago. Ten percent said they were undecided, and 58 percent were against.

In the Sept. 18 WBUR/MassINC poll, 44 percent opposed the question, 44 percent supported it and 12 percent were undecided.

The phone survey of 502 likely voters was conducted from Oct. 25 through Oct. 28 over both landlines and cellphones. It has a 4.4 percent margin of error.

With Gov. Charlie Baker and U.S. Sen. Elizabeth Warren both posting strong leads over their challengers in all polling released so far this election cycle, the nurse staffing ballot fight has become the most heated contest as both sides pour millions into ads and stage events with direct care providers.

On Thursday, Boston Mayor Martin Walsh plans to join a Yes on 1 rally at Faneuil Hall, along with Massachusetts AFL-CIO President Steve Tolman and American Federation of Teachers President Randi Weingarten.

Backers of the question have spent $10.4 million, and opponents nearly $17.6 million, according to the state Office of Campaign and Political Finance.

The breakdowns have remain largely unchanged for each of the other two questions on the Nov. 6 ballot, the new poll shows.

On Question 2, which asks voters to create a commission that would advance a constitutional amendment to limit the influence of money in politics, 64 percent said they'd vote yes and 27 percent no. Last month, 66 percent backed the measure and 24 percent opposed.

Question 3 is to uphold or repeal the state's two-year-old transgender non-discrimination law. The new poll had 68 percent in favor of keeping the law and 26 percent for repeal, compared to 71-21 last month.