Union members will pay dues equal to 2.5 hours of regular monthly pay, up from two hours a month.

In a rare divisive debate at the UAW convention, where most resolutions are passed by near-unanimity, 20 delegates spoke for and 20 against the measure.

After a voice vote was declared by UAW President Bob King to be too close to call, a show of hands in the downtown Detroit convention hall showed support for the union. It appeared that nearly a third voted against the dues increase.

Tuesday's vote came as the auto industry reported an annual U.S. sales rate in May that was the strongest since before the 2008 recession. Nearly half of the UAW's 400,000 members are in the automotive industry, including workers at the largest three U.S.-based automakers.

A veteran UAW-represented worker at either General Motors Co , Ford Motor Co, or Fiat Chrysler Automobiles making about $28 per hour will pay union dues of about $70.32 per month, up from about $56 currently. A recently hired worker making $15.78 per hour will pay $39.45 per month, up from the current $31.56.

King, whose four-year term as head of the union ends later this week, campaigned for the dues increase for more than six months. He said the hike was needed because the union's strike fund had shrunk to around $600 million from more than $1 billion a decade ago.

The UAW says the dues increase will raise about $49 million a year.

Gary Walkowicz, from a Ford plant in Dearborn, Michigan, called for the vote to be forestalled to allow to allow a referendum of the union's full membership. But King said one of the reasons a full referendum was not being held was that anti-UAW "outside influences" would affect the vote.

While the UAW's membership has increased 10 percent during King's four-year term, it is down 40 percent from about 655,000 a decade ago. The union had nearly 1.5 million members at its peak in 1979.

Dennis Williams, the UAW's secretary-treasurer, is expected to be voted in as the union's new president by delegates at the convention on Wednesday. He is opposed by Walkowicz, who is not expected to get much support.

The dues increase goes into effect in August.

"A strong strike fund is the best defense against being run over by the companies," said Bill Lucas, who works at an auto parts distribution plant in Ohio, echoing a view shared by many delegates.

But others, like Edd McNulty, from a GM plant in Ohio, said delegates were voting against the majority of the UAW's membership.

"The leadership (of the UAW) has lost touch with the people who work on the shop floor," said McNulty.