Denver ? Seven environmental groups endorsed ballot measures Tuesday that would relax state spending limits, saying the caps threaten Colorado’s ability to safeguard air and water quality and preserve open space.

“A vote for Referenda C and D is a vote for clean air in Colorado,” said Will Coyne of Environment Colorado.

Other speakers at the news conference along the South Platte River said state budget constraints have affected the state’s efforts to enforce clean air and water regulations. Elise Jones of the Colorado Environmental Coalition noted that the Environmental Protection Agency has said the Colorado Water Quality Control Division has far fewer staffers than states of comparable size. The EPA has said the staff shortages don’t threaten public safety.

“Colorado should not have to bankrupt the quality of its drinking water,” Jones said.

Besides the environmental groups, a bipartisan coalition of political and business leaders supports the two items on the November ballot.

Referendum C would lift the caps in the Taxpayer’s Bill of Rights, a constitutional amendment, for five years and allow the state to keep $3.1 billion in tax revenue that would otherwise be refunded to taxpayers.

Referendum D would allow the state to borrow up to $2.1 billion for roads, school maintenance, pensions and other projects.

The measures’ supporters contend that TABOR, which requires voter approval of tax increases, has hamstrung the state. They argue the formula that determines how much revenue governments can keep and spend creates a “ratchet-down” effect.

Opponents respond that the ballot measures amount to a tax increase and contend that suspending TABOR will harm the economy.