A national nurses union and Southeast Side activists will call on Mayor Rahm Emanuel today to ban petroleum coke in Chicago city limits until the piles of dust are enclosed.

National Nurses United says in a news release that an Emanuel-backed ordinance the City Council passed last month to regulate storage of petroleum coke doesn't go far enough.

The union wants the city to enact a moratorium on all petroleum coke storage, transport and other operations "until it is learned what impact petcoke has on the health of Chicagoans or until the piles are enclosed," according to the release.

Union members will tour the petroleum coke facilities with people who live nearby, then deliver a letter to Emanuel at City Hall telling him he needs to go further in regulating the product, which is the residue from the refining of heavy crude derived from tar sands.

The mayor has repeatedly said the city does not have the legal authority to entirely outlaw petroleum coke, which sparked protests after the dust began coating the neighborhoods near the facilities on the Southeast Side.

The rules aldermen enacted require three existing petroleum coke terminals along the Calumet River to enclose their piles within two years, and to submit quarterly reports on the amount of the product shipped in the city.

Emanuel aides said the restrictions will give Chicago the nation's toughest limits on black mounds of petroleum coke rising near refineries that are shifting to thicker, dirtier oil from the tar sands region of Alberta.