Nevada's powerful labor unions are backing Lee

While O'Donnell has help from Republicans' national war chest, Lee has the support of the political powerhouse that is the Culinary Workers Union, representing 60,000 hospitality workers in Nevada.

Secretary-Treasurer Ted Pappageorge said the current "no tax on tips" policy brings some relief but is "deeply flawed." A married couple filing jointly can deduct only up to $25,000 of their tipped income, Pappageorge said. The policy also does not apply to automatic gratuities that are charged to large parties, he said. Lee and other Nevada Democrats want to fix that, he said.

"There's a history of our Democrats here fighting for fair taxation," Pappageorge said.

On a recent weekend in Lee's district about 50 days before the election, members from the Culinary Union, the American Federation of Labor and the Congress of Industrial Organizations knocked on voters' doors, hoping to sway those still undecided.