Los Angeles — The nation's most populous county could lift the minimum wage for some workers to $15 an hour by 2020, just weeks after the city of Los Angeles took a similar step to fatten paychecks for employees at the lower-rung of the economy.

The Los Angeles County Board of Supervisors is expected to take a preliminary step Tuesday that could lead to the higher wages. A proposal would direct county lawyers to draft a proposed law gradually increasing the wage mark over several years, which the board would consider later this year.

If approved, the hourly wage would increase in steps until it hits $15 in 2020. Then, beginning in 2022, the wage would be increased annually based on inflation, according to the proposal.

The vote is expected a day before Vice President Joe Biden travels to Los Angeles to promote a higher minimum wage as a way to lift more Americans toward the middle class.

Endorsement of the plan by the county board would be seen as a strong signal that it will approve the $15 hourly benchmark.

However, the proposal would only have a limited effect in a county with nearly 10 million people. It would apply to scattered, unincorporated areas of the county that are outside its 88 cities, along with a slice of county workers who earn paychecks below that level.

Smaller companies would have until 2021 to meet the higher pay mark.

Labor and other supporters of high minimum wages hope the county's endorsement would encourage other cities to join Los Angeles with higher hourly wages.

Democrats are hoping to make support for higher minimum wages a campaign issue in 2016.

Seattle and San Francisco also are gradually raising their minimum wage mark to $15 an hour. St. Louis is considering a similar measure.

Earlier this month in Sacramento, a legislative committee advanced a proposal that would raise California's statewide minimum wage to $13 in 2017, then tie the minimum wage to inflation starting in 2019. The California Chamber of Commerce has said the bill would lead companies to slow hiring.