In a 200-page report out today, HRW found that the retail giant stands out for the magnitude and aggressiveness of its anti-union tactics.
HRW senior researcher Carol Pier said: 'Wal-Mart workers have virtually no chance to organise, because they're up against unfair US labour laws and a giant company will do anything to keep unions out. [Wal-Mart] devastates workers' right to form and join unions.'
Wal-Mart is the largest private US employer, with 1.3 million workers. It made sales of US$351.14 billion (£175.35 billion) and profits of US$11.3 billion (£5.64 billion) in the fiscal year to January.
The HRW investigation said Wal-Mart indoctrinates workers and managers to oppose unions from the moment they're hired. The charity said managers receive explicit instructions on keeping out unions, many of which are found in the company's Manager's Toolbox - a guide to managers on 'how to remain union free in the event that union organisers choose your facility as the next target'.
The group has demanded Wal-Mart ceases all tactics, both legal and illegal, that undercut workers' right to organise. HRW has also called for the retailer to pledge a neutral stance on union formation.
In its response to the investigation, Wal-Mart said the charity has produced a 'pro-union' report and used 'incomplete interviews and unsubstantiated allegations from as much as six to seven years ago'.
The United Food and Commercial Workers (UFCW), a US union, also recently launched a campaign against the UK's biggest supermarket Tesco ahead of its US debut later this year, claiming the retailer promotes underage drinking. However, it is thought the union's protest is part of a wider campaign to ensure Tesco workers in the US will get recognised union representation, unlike rival Wal-Mart.