Courting the labor vote in eastern Iowa, Hillary Clinton said Monday she would "go back" to enforcing the nation's labor laws, pledging to send employers to jail who are guilty of wage theft.

Clinton, the former secretary of state, made stops in the Quad-Cities, Cedar Rapids and Burlington on Labor Day, campaigning amid a shrinking lead in the polls.

In a 15-minute speech at the Salute to Labor picnic in Hampton, Ill., Clinton said she'd push for paid family leave, raising the minimum wage and seek higher incomes for all, the latter what she called the country's "defining" economic challenge.

But she also suggested that she'd take a more aggressive approach to dealing with wage theft, a frequent complaint of unions who say weakened employees are frequently short-changed compensation by employers. 

"We're going to go back to enforcing labor laws, and I'm going to make sure that some employers go to jail for wage theft," she said.

Clinton also pointed to Wisconsin Gov. Scott Walker's and Illinois Gov. Bruce Rauner's battles with labor unions and said it required more than just complaints, but winning political campaigns.

"We can't just wring our hands and argue about it. We've got to organize ourselves, and we have to make Republicans pay the price at the polls," she said.

Overall, Clinton argued she was the one who had the policies and the tenacity to enact change.

The crowd at the picnic was larger than normal for Clinton's appearance, the first by a presidential candidate there since Vice President Al Gore visited in the late 1990s.

Clinton was joined by Sen. Dick Durbin, D-Ill., and Reps. Dave Loebsack, D-Iowa, Cheri Bustos, D-Ill., and Tammy Duckworth, D-Ill.

Loebsack formally endorsed Clinton, praising her as experienced and committed to working people. Bustos, meanwhile, told the crowd, "we need to stand with Hillary Clinton."

Not on stage, but in the crowd, was former Rep. Phil Hare, who said he is backing Sen. Bernie Sanders.

Much of the Salute to Labor crowd is from Illinois. The event is sponsored by the Rock Island County Democratic Party, though it also draws Democrats from Iowa.

Mary Lind, of Moline, said she saw an energized Clinton she believes is often obscured by a biased media. "I was worried about her energy and her fire in the belly. But I didn't see a lack of that today," she said. "That was very reassuring to me."

In recent polls in Iowa, Clinton has seen her lead Sanders narrow. An NBC News/Marist poll, released over the weekend, said that 48 percent of likely Democratic caucus-goers in Iowa backed Clinton, compared with 37 percent for Sanders.

In July, Clinton led Sanders by 24 points.

The closer contest comes as Clinton has faced questions about her exclusive use of a private email account while secretary of state.

In an interview Monday with the Associated Press in Iowa, Clinton defended herself, saying, "What I did was allowed. It was allowed by the State Department."

The email controversy has worried some Democrats, including in Iowa, who fear it will weigh on her election chances.

Karen Betcher, of Osco, Ill., said she too worried it would hurt her in the election. But she said she backed Clinton because she trusts her. And she blamed Republicans and the news media for the controversy.

"I don't believe there was anything that she did that was wrong," Betcher said.