Amazon to raise the national average wage for contracted delivery drivers from $20.50 to about $22 an hour, the company said Thursday.

The pay increase is part of the $2.1 billion Amazon is investing this year in its delivery partner program, a variety of contract companies that handle the last mile of package delivery from the company’s warehouses to customers’ doors.

The company’s announcement comes at a time when it is facing renewed unionization among its contract suppliers.

Beryl Tomay, Amazon’s vice president of transportation, wrote in a blog post that many DSPs are already paying “well above” $22 an hour. The increased rates will continue to support DSPs “in their efforts to recruit and retain high-performing teams.”

Amazon announced the raise at the same time it is hosting an annual, closed conference for these delivery service providers called Ignite Live in Las Vegas. The company made a similar announcement at last year’s event. Amazon says it has enrolled more than 3,500 DSPs in the program since it launched in 2018.

The Teamsters Union has led several strikes at Amazon delivery facilities over the past year and has made organizing Amazon workers a central focus after forming a dedicated division for the online retail giant in 2021.

The National Labor Relations Board has also been scrutinizing the company’s relationship with its contract suppliers. Since August, the federal labor agency has issued two rulings that Amazon should be considered a “joint employer” of employees at two subcontracting companies. The NLRB’s decision could force Amazon to negotiate with employees who want to form a union.

Amazon has resisted being classified as a joint employer of its contracted delivery drivers, arguing that the workers are employed by third-party companies. Politicians and labor groups have challenged the company’s classification, saying the drivers wear Amazon-branded uniforms, drive Amazon-branded delivery trucks, and their work hours and performance expectations are set by Amazon.

The company has previously stated that it disagrees with the NLRB’s findings.