Donald Trump s project that is supposedly converting the Old Post Office building in Washington, D.C. is the subject of a Labor Department investigation. It is being alleged that workers on the site are being paid less than what is mandated under federal law.The Labor Department confirmed to POLITICO that it s looking into allegations of wage-rule violations by the Craftsmen Group, a Trump Organization subcontractor that restores windows. And workers on the site, including one Craftsmen Group employee, told POLITICO that they and others aren t receiving pay rates mandated by law. Two of them produced pay stubs to support their claims.Trump s refurbishment of the Romanesque pile, built in 1899, into a luxury hotel is his highest-profile real estate project, if only because the historic structure is situated just a few blocks from the White House. Trump staged a campaign event at the construction site in March, blending presidential politics with commerce.  When it s completed,  he said,  it will be truly one of the great hotels of the world. Trump s contract with the federal government for the site is actually structured so that Trump is actually leasing it from the government. That means wages on the site are set by federal law, which requires all workers   union or not   on the site to be paid the  prevailing wage  set in the area by labor unions.A sign at the Trump site pointed out that glaziers, the workers installing shower doors, should be paid between $24.30 to $27.64 an hour. But their paystubs show them earning way less   between $13 to $16 an hour   almost half of what the law requires.Trump has been slammed recently for repeatedly underpaying contractors who have done work on his properties, and in some instances not paying them at all for the work they ve done for him and his companies. Trump claimed that he was completely justified in stiffing workers.Featured image via Flickr