Measure 7, approved by 53% of voters in November, requires "payment to landowner if government regulation reduces property value." It's supporters say it will cost government no more than $50 million to $100 million per year. It's opponents put the annual impact at closer to $5.4 billion because they believe that as many as 90 types of laws - from building height limits to requirements for public restrooms to solid waste disposal restrictions - may qualify for Measure 7 claims.

To get the preliminary injunction, lawyers must convince the judge that Measure 7 would cause "irreparable damage" if allowed to take effect, and that their lawsuit has a "substantial likelihood of success" at trial. Judge Paul Lipscomb's ruling was in response to a lawsuit filed last week by the mayors of Salem and Jacksonville, and Audrey McCall, widow of former Gov. Tom McCall, who is credited with designing Oregon's vaunted system of land-use and environmental rules. A second lawsuit challenging the measure's constitutionality was filed Tuesday in Marion County Circuit Court by the League of Oregon Cities and others.

All of the legal challenges to Measure 7 are technical in nature. One argument is that it contains two or more "substantive and not closely-related" changes to the constitution and therefore violates the constitution's "single subject" rule for amendments. Another is that the measure itself does not contain the "full text" of the amendment, and a third is that the measure is not a proper amendment because it is advisory in nature.