According to an in-depth report by ProPublica, workers at some of New York’s most expensive apartment buildings are being underpaid by developers and landlords.

The problem centers around buildings that benefit from the city’s 421-a program, which grants $1.1 billion in tax breaks every year to developments that include a certain number of affordable units. Under the law, employees of these developments must be paid a “prevailing wage,” which is tied to the wages of union workers. So in essence, non-unionized workers at 421-a buildings must be paid the same rate as their unionized counterparts.

The law is supposed to be enforced by the City Comptroller’s office, which can revoke the tax breaks if landlords and developers don’t comply. However, city officials have been lax in their enforcement – and as a result, many workers are being underpaid.

ProPublica interviewed a doorman at a luxury building in Long Island City who’s making $10 per hour when he should be making 70 percent more, plus additional benefits. Meanwhile, the building he works for received almost $1 million in tax breaks under the 421-a program.

While the Hudson Yards development has benefited from the 421-a tax break, it’s unknown whether workers there are being paid fairly. The Department of Housing Preservation and Development (HPD), which administers the 421-a program, has refused to release the list of 421-a recipients covered by the “prevailing wage” requirement.

“As is, it’s up to workers to bring wage-theft allegations to the attention of authorities. But employees are caught in a Catch–22: They often have no idea that they’re entitled to the prevailing wage, and finding out if they are isn’t easy,” ProPublica reports.