DULUTH, Minn. — A Duluth head shop owner was back in court again, this time to ask that a city ordinance aimed at regulating sales of synthetic drugs be declared unconstitutional.

Attorney David Malban, who represents Jim Carlson, owner of the Last Place on Earth, asked U.S. Magistrate Judge Leo Brisbois on Friday to prevent the city from enforcing the ordinance. He said the law, which took effect Thursday, is unconstitutional because Carlson would be forced to incriminate himself if he applied for a license.

Two attorneys for the city disputed that.

The Duluth News Tribune reports (http://bit.ly/15oQgA2 ) Brisbois said he'll rule by noon Monday.

It's one of a half-dozen pending legal actions involving Carlson — civil and criminal — stemming from sales of synthetic drugs at the Last Place on Earth.