By David Shepardson

(Reuters) -General Motors said Thursday it has offered workers a 10% wage hike and two additional 3% annual lump sum payments over four years in its offer to the United Auto Workers union ahead of the Sept. 14 contract expiration.

Last week, Ford said it had offered a 9% wage increase through 2027 and 6% lump sump payments, much less than the 46% wage hike being sought by the union.

GM said the wage hike is the largest proposed since 1999. It is also offering a $6,000 one-time payment and $5,000 in inflation-protection bonuses over the life of the agreement, along with a $5,500 ratification bonus.

Chrysler-parent Stellantis said Wednesday it planned to make a counteroffer to the UAW this week.

GM said that under its offer, current temporary employees will receive a 20% increase to $20 per hour wage and it would shorten the time it takes to get to the maximum wage rate for permanent employees.

"We still have work to do, but we wanted to make this offer to show our good faith efforts to keep the process moving," GM said in a letter to employees.

Last week, the UAW filed unfair labor practice charges with the National Labor Relations Board against GM and Stellantis saying they refused to bargain in good faith.

The union's demands include a 20% immediate wage increase followed by four 5% annual wage hikes, defined-benefit pensions for all workers, 32-hour work weeks and additional cost of living hikes.

(Reporting by David ShepardsonEditing by Nick Zieminski)