The state’s senior U.S. senator, progressive darling Elizabeth Warren, yesterday said she is still undecided about the major labor issue looming over the Bay State this fall: the ballot question lifting the cap on the number of charter schools statewide — a petition that has drawn fervent opposition from unions and teacher associations.

“I’ve raised issues about this one,” she said. “First, I want to get more information from these guys as we go along. There are people out there who are spending a lot of money, and it seems to be a lot of people not from Massachusetts are spending a lot of money to push through some of these ballot initiatives.

“And boy, I don’t know about you,” she told reporters, “but that kind of raises the hair on the back of my neck.”

Warren made the comments after she delivered a speech at the Greater Boston Labor Council’s annual Labor Day breakfast dedicated to opposing the measure that would allow for 12 new or newly expanded charter schools a year, with dozens of posters covering a Park Plaza Hotel ballroom calling for a “no” vote on Question No. 2.

With one of the signs serving as the stage’s backdrop, Warren took to the podium saying she owes a “huge thank you” to several union officials she said have “my back when I’m down in Washington.”

“I want you to know,” she said, “I do my best to have your back, too.”

The Democratic State Committee voted last month to oppose the ballot question, prompting Mara Dolan, the communications director for Senate President Stanley C. Rosenberg, to insinuate in a tweet that “real Democrats” don’t support it. Mayor Martin J. Walsh, once a charter school board member, has also come out in opposition.

Warren said she has “worries” about the charter question, but she didn’t commit to opposing it. Asked by reporters to say how she’ll vote on all four questions slated to go before voters in November, Warren gave a flat “no.”

“I’m still working on some of them,” she told reporters.

U.S. Sen. Edward J. Markey, Warren’s Bay State colleague in Washington, indicated he will vote against the charter school measure, saying he is “very skeptical” of it and is concerned that if passed, it would “drain” the state public school system of too much money.

“I’m leaning against Question 2,” he said.