Manhattan’s retail rent rollback is causing Wal-Mart to give the city another look.

The giant discount chain has shopped for space in Union Square and among the big-box stores along Sixth Avenue in Chelsea, The Post has learned.

Wal-Mart recently passed on a proposal by Related Companies for a two-level store of about 57,000 feet in Union Square where Virgin Megastores and Circuit City are closing, sources said.

The company’s real-estate scouts have also been roaming the area around 620 Sixth Ave., said the sources.

Wal-Mart spokesman Steven Restivo said the Union Square sites “were never under consideration.” But he said the company is “still interested” in opening stores in New York, despite strong political and union opposition.

Unions say that despite the city’s economic distress, it doesn’t need the retail giant.

“We don’t need Wal-Mart to take advantage of an economic crisis to sneak into New York and drive down standards and wages,” said Stuart Appelbaum, president of the Retail, Wholesale and Department Store Union.

The retailer says it offers good jobs – its average wage for full-time workers elsewhere in New York is $11.62 an hour, and it offers 401(k) plans.