Amazon is raising the average national hourly wage for contract delivery workers from $20.50 to about $22 per hour, the company said Thursday.

The pay increase is part of Amazon’s $2.1 billion investment this year in its delivery partner program, the dozens of contracted companies that make final deliveries of packages from the company’s warehouses to customers’ doorsteps.

The company makes the announcement as it faces a renewed push to unionize its delivery workers.

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 higher rates will continue to support DSPs “as they seek to recruit and retain high-performing teams.”

Amazon announced the pay increase at the same time it’s hosting an annual, private conference for those delivery contractors, called Ignite Live, in Las Vegas. The company made a similar announcement at last year’s event. Amazon has said it has added more than 3,500 DSPs to 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 major focus after creating a chapter specifically focused on the online retail giant in 2021.

The National Labor Relations Board has also been scrutinizing the company’s relationship with its contracted delivery workers. Since August, the federal labor agency has issued two rulings holding that Amazon should be considered a “joint employer” of workers at two subcontractors. The NLRB’s ruling could force Amazon to negotiate with workers who want to unionize.

Amazon has fought to avoid being designated as a joint employer of its contracted delivery workers, arguing that the workers are employees of outside companies. Lawmakers and unions have challenged the company’s characterization, saying that drivers wear Amazon-branded uniforms, drive Amazon-branded vans, and that their schedules and performance expectations are set by Amazon.

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