(Reuters) - Colorado’s Supreme Court on Monday struck down voter-approved bans on fracking and the storage of fracking waste within the cities of Fort Collins and Longmont, ruling they conflicted with state law.

Voters in Longmont approved a ban in 2012, while voters about 30 miles north in Fort Collins approved a five-year moratorium in November 2013, drawing legal challenges from the Colorado Oil and Gas Association, an industry trade group.

Lower courts subsequently sided with the association, invalidating the Fort Collins moratorium and the Longmont ban.

The Colorado Supreme Court affirmed the rulings in separate decisions. Justice Richard Gabriel said the Longmont ban could result in uneven and potentially wasteful oil and gas production and affect the rights of the owners of those interests.

The decisions in Colorado are the latest rulings on attempts to curb the hotly contested oil and gas extraction process known as fracking through popular votes.

In Denton, Texas, for example, voters approved a hydraulic fracturing ban in 2014 that prompted lawsuits by a Texas industry trade group and bills in the Texas legislature that eventually led to a state law that prohibited cities from interfering.

The Colorado Supreme Court found the Longmont ban and Fort Collins moratorium operationally conflict with the application of the state’s Oil and Gas Conservation Act.

If left in place, the Longmont ban “could ultimately lead to a patchwork of regulation that would inhibit the efficient development of oil and gas resources,” Gabriel wrote.

As was the case with the Longmont case, Gabriel said, the Fort Collins moratorium would render the state’s statutes and regulatory scheme superfluous for at least a lengthy period, materially impeding Colorado’s interests in efficient development of oil and gas resources.

Gabriel noted that proponents of fracking tout the economic advantages of extracting previously inaccessible oil and gas and opponents warn of health risks and environmental damage, but he said the cases did not hinge on deciding if either side was correct.

Dan Haley, chief executive of the Colorado Oil and Gas Association, said the rulings send a strong message. “Bans and moratoriums on oil and gas are not a reasonable or responsible way to address local concerns,” he said.

The Sierra Club, which intervened in the Longmont case, called the decisions deeply unsettling.