DENVER—Colorado’s free-wheeling constitutional amendment process is under attack again by state lawmakers from both parties.

The state Senate voted 27-8 Friday to give preliminary approval to a measure that would make it harder to change Colorado’s constitution.

Colorado has the nation’s lowest signature threshold to petition an amendment onto ballots, accounting for the state’s small population. The current requirement is about 86,000 signatures.

Policy-makers say Colorado’s constitution had been amended 81 times in the last 44 years and is riddled with confusing amendments.

“I am embarrassed to see how many changes are in our constitution,” said Democratic Sen. Linda Newell of Denver.

Republican leaders, including the Republican House Speaker, have signed on to the idea, too. In Friday’s Senate debate, Republican Sen. Nancy Spence argued that while the state needs to preserve the public’s ability to change the constitution, the process is too easy.

“These low threshold requirements, together with our small population, make Colorado an ideal place for special interests . to use Colorado as a testing ground,” she said.

The measure would raise the threshold to 60 percent, instead of a simple majority, for a constitutional amendment on ballots to pass, starting in 2013. It also requires that petitions include voters from various parts of the state to sign a petition, a change to prevent one region from pushing a measure another region opposes. Previously adopted constitutional amendments could still be repealed with a simple majority.

If the measure passes the Senate and then the House, as appears likely, the change would head to Colorado voters next year. But a similar measure was rejected in 2008, and a handful of Republicans voted against this year’s change, saying voters don’t like the idea of making it harder to change the constitution.

“What we have before us here is an attempt to strip the authority and the ability of the citizens to change the constitution,” Republican Sen. Kevin Lundberg argued.

Democratic Gov. John Hickenlooper this week called the state’s confusing amendments a “huge issue.” But when a group of newspaper publishers gathered for a Colorado Press Association meeting asked Hickenlooper how the ballot initiative process should be changed, the governor wouldn’t say. It’s unclear whether he’d sign the measure.

“I’ve got opinions, but I didn’t want to go out and, before we even get started, and color everybody’s perception,” Hickenlooper said.

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Online:

Read Senate Concurrent Resolution 1: http://goo.gl/ly5JX