"The lawyers argue that the two-thirds requirement has been undermined by more recent decisions of the state's high court. In particular, they contend, the court's May 2009 ruling on same-sex marriage defined the limits on voters' power to amend the California Constitution by initiative, and showed that a change as far-reaching as the two-thirds requirement exceeds those limits.
The requirement 'upsets the bedrock principle of lawmaking by majority rule upon which the California Constitution was founded,' attorney William Norris said in papers filed with a state appeals court in Los Angeles."
If the lawsuit is successful, it will change the rule of the 1978 law to allow simple majority voting to change state taxes, but would not change the current provisions limiting increases in property taxes.
Thanks to Nate Berg