The Colorado Public Utilities Commission has passed rules that could make it more difficult and more expensive to build new natural gas pipelines or extend existing ones in the state. The rules require regulators to sign off on any pipeline construction plans by natural gas utilities with more than 90,000 customers. Utilities would have to pay the full costs of pipelines up front. Democratic Gov. Jared Polis has set a goal for natural gas utilities to reduce greenhouse gas emissions by 4 percent by 2025 and by 22 percent by 2030.