Amazon will give a pay rise of up to $3 an hour to more than 500,000 employees in its US logistics network, amid continued scrutiny of working conditions for its frontline employees.

The online retailer on Wednesday said it had brought forward its annual pay review and would incrementally increase wages from between $0.50 and $3 per hour — an investment of $1bn, according to Darcie Henry, Amazon vice-president.

“This is on top of our already industry-leading starting wage of at least $15 an hour and the more than $2.5bn that we invested last year in additional bonuses and incentives for front-line teams,” Henry said in a statement.

The company said it was hiring “tens of thousands” of jobs in its vast logistics network, having already rapidly expanded during the pandemic, bringing its workforce to more than 800,000 in the US alone, making it the country’s second-largest employer, behind Walmart.

The pay rise did not apply to the company’s workers outside of the US, a spokeswoman said.

Amazon employees in the country currently start on at least $15 per hour, more than double the national minimum wage. But the jobs, and the use of tightly monitored productivity quotas, have drawn fierce criticism from campaigners and politicians, particularly as the dangers of coronavirus set in.

In March 2020, during the frantic early stages of the pandemic, Amazon temporarily increased pay from $15 to $17, but dropped the increase several months later.

The latest move comes 13 days after Jeff Bezos, chair and chief executive, in his annual letter to shareholders, acknowledged the company needed to improve its relationship with employees, following a bitter unionisation drive at an Amazon warehouse in Bessemer, Alabama.

Workers at the plant overwhelmingly voted against joining a union earlier this month but the campaign threw a spotlight on workplace conditions. Amazon has also been accused of unfair influence on employees during the ballot process and a hearing on the union’s challenge to the result is due next week.

In his letter, Bezos wrote: “Does your chair take comfort in the outcome of the recent union vote in Bessemer? No, he doesn’t. I think we need to do a better job for our employees.

“While the voting results were lopsided and our direct relationship with employees is strong, it’s clear to me that we need a better vision for how we create value for employees — a vision for their success.”

The effort in Alabama has spurred union activity at the company in other parts of the country, with a renewed focus on the conditions faced by about 50,000 Amazon delivery drivers.