A week after she pilloried Walmart at a February hearing, City Council Speaker Christine Quinn welcomed executives from the retail giant, which is seeking to open its first stores in the city, into her lower Manhattan office for a chat. And despite shelving paid sick days legislation last year, she continues to talk with its sponsor, Councilwoman Gale Brewer, about reviving it. Bills to mandate higher wages at city-subsidized projects will soon present her with other controversial choices.

With the 2013 mayoral race looming, Ms. Quinn has been straddling contentious issues that pit the business community against her progressive base. But she cannot walk the tightrope forever.

“In New York, you have to walk a fine line to get elected in a Democratic primary,” said George Arzt, a veteran political consultant. “And she’s walking that line.”

Which side she chooses will determine the fate of so-called living wage requirements, mandatory sick pay and other measures opposed by the business community and her most visible ally, Mayor Michael Bloomberg. The speaker can stop bills in their tracks or direct her members to override mayoral vetoes.

Ms. Quinn, who declined to be interviewed for this story, said in a statement that government’s job is “to bring stakeholders together to build consensus and find real solutions to the city’s problems.” When she put paid sick days on the back burner, she said, “I made a decision that was not easy, based on the requirements of the job” and not based on “any future race.”

The speaker is both an “expedient politician and core believer,” said Doug Muzzio, a professor of public affairs at Baruch College. “A dominant element of her decision-making is certainly political, but it’s not necessarily the only element all the time, every time.” Those close to her insist that the mayoral race, which she is widely expected to enter, is not a big factor in her decisions.

For Ms. Quinn, political calculations can be the toughest part. She’s a former tenant activist with a progressive past, but her alliance with the mayor raises questions about what her path to victory might be in 2013.

She enjoys support from the business community, which is largely responsible for the $3.2 million in campaign cash she has collected in the past four years. Mr. Bloomberg is certainly a fan—a Democratic consultant said (disdainfully) that the mayor’s team thinks of the speaker as staff—but as his popularity sags, his imprimatur could become a hindrance.

Cultivating constituencies

Still, the mayor can help Ms. Quinn behind the scenes. A Democratic insider said that former Bloomberg campaign manager Bradley Tusk, a consultant for Walmart, is telling some clients to get on board with Ms. Quinn. (Mr. Tusk said only that he’s setting up meetings for his education reform clients with Ms. Quinn.)

The speaker has been moving to cast herself as independent of Mr. Bloomberg. But even if she bucks her business supporters by opposing Walmart’s attempts to open a city store and backing living wage and paid sick days, insiders said, the most crucial labor unions and the Working Families Party would still support Public Advocate Bill de Blasio or Comptroller John Liu for mayor, should either one run.

Instead, campaign experts said, Ms. Quinn must assemble a patchwork of constituencies: small business, gays and lesbians, women, building trades, tenant activists and African-Americans. Smoothing Walmart’s arrival would help her with the building trades and some black voters, who want the jobs the retailer would bring.

Which way on Walmart?

“She’s talked to Walmart and to the unions, and clearly she’s looking for middle ground,” Mr. Arzt said. “Most people are going to be wary about losing jobs by preventing Walmart from coming in.”

Stuart Appelbaum, president of the Retail, Wholesale and Department Store Union, thought otherwise. “Even after she met with Walmart, she said they didn’t convince her, and she’s still opposed,” he said.

Ms. Quinn has been unyielding in her criticism of Walmart’s labor practices, but food policy offers the chance for a deal. Her FoodWorks initiative to bring fresh, healthy and affordable food to all New Yorkers needs corporate partners—a bill Walmart could fill. Walmart has repeatedly said it would focus on poor, underserved neighborhoods that lack fresh food options.

The retailer has teamed up with first lady Michelle Obama on a plan to build stores in poor neighborhoods and sell healthier foods. A similar alliance with Ms. Quinn, while sure to upset retail and supermarket unions, would make a splash and could pay off in 2013.

The way forward on living wage is less clear, because there is a broader array of supporters and opponents. The bill is before the council and a city-funded study on the issue could be released any week now, so Ms. Quinn will have to take a position. The mayor, the real estate industry and an alliance led by the city’s chambers of commerce oppose wage mandates. Several groups, including Mr. Appelbaum’s union, the powerful 32BJ SEIU building service workers, and a community and clergy coalition, back the measures.

When Ms. Quinn waylaid the paid sick days bill, she cited the recession but left open the possibility of changing her mind if the economy improves—which it has.

Some insiders said that the controversial issues she tackles as speaker will prepare her for a competitive campaign, and that New Yorkers want to see their leaders make hard choices.

“I honestly believe she tries to make the best decision, not based on polling, popularity or endorsements,” said Pat Purcell, assistant to the president of United Food and Commercial Workers Local 1500.

With key business issues coming to a head, there’s plenty of decision-making to come.