A bipartisan group of 144 lawmakers has delivered an open letter to the US Government calling for the reinstatement of subsidies for wind power generation.

In the letter, legislators led by senators Mark Udall (Democrat) and Chuck Grassley (Republican), and representatives Steve King (Republican) and Dave Loebsack (Democrat), warn that the wind industry – including 559 factories involved in manufacturing parts for turbines – is under threat due to the policy uncertainty.

The production tax credit (PTC) and investment tax credit (ITC) expired at the end of last year, leaving the country without a national subsidy system for wind power, reports Wind Power Monthly.

The signatories urged policy "certainty and predictability so that long-term project decisions and investments can be made."

At the start of 2013, the government passed an extension of the subsidies and a change in the conditions to allow projects under construction, rather than only those generating power, to qualify. This led to a boom in projects under construction at the end of last year.

However, it is feared that if a subsidy regime is not reintroduced, this increase in construction could prove little more than a spike. Installations in 2013 fell 92% due to the anticipation of a policy gap.

The PTC provides up-front tax relief of $0.023 per kilowatt hour for the first ten years of a project, while the ITC allows the claiming back of 30% of initial investment in a project. Developers could only qualify for one of the subsidy schemes.