Amazon is making increases in wages for hourly workers across the United States.

Amazon is spending nearly $1 billion boosting wages for hourly workers in the US amid criticism of its labor practices and a pitched union battle.

The increase will take the starting wage for most front-line warehouse and transportation employees to over $19 an hour, while pay in fulfillment and elsewhere will rise to $16 an hour.

The company said the minimum wage would remain at $15 an hour.

Amazon is currently offering employees the option to access up to 70 percent of their eligible pay at any time without a fee, instead of the usual once or twice a month option.

It also added a new development program, which allows employees to advance to engineering roles after 12-14 months of training.

Amazon.com is the second-largest employer in the US after Walmart.

Most of those workers are in the warehouses or at Whole Foods or Amazon Fresh.

According to the Bureau of Labor Statistics, the average hourly pay in the United States is $32.36.

In April of this year, 8,000-plus workers at a Staten Island facility voted to unionize, and Amazon lost its initial appeal for a re-vote.

The city is also facing a House committee probe into a deadly warehouse collapse that killed six workers during a tornado.

In June, the panel accused Amazon of "obstructing" the investigation by refusing to hand over key documents related to an internal review.