The groups called on the commission to put pressure on national governments to clarify and simplify permitting procedures for renewable energy projects.
"Permitting rules and procedures for new and repowered renewable energy projects remain too complex and lengthy," the letter stated.
For the wind industry, permitting bottlenecks have hampered major markets such as France and Germany, placing many companies in a precarious position, even before the health crisis swept the globe.
The EC had directed member states to address permitting concerns as part of their National Energy and Climate Plans (NECPs). However, most governments were silent on the issue.
"This is a red flag for the industry. Without an appropriate and simplified framework for permitting, the 2030 national renewable energy commitments remain purely academic," the trade bodies wrote.
They called on the EC to remove the permitting bottlenecks by ensuring member states enforce rules that would allow for a shorter process, and to audit member states to establish if they have the necessary human resources to handle permit applications efficiently.
The letter also said the EC should "clarify with member states that there are no barriers in EU law that forbid changes in the technology specifications in the timeframe between the permit application and the construction of a renewable energy project. Member states should support renewable energy operators in deploying the most efficient technology available for a specific site."
In many countries, particularly France, developers are unable to alter the technical specifications of a project, even though permitting takes several years, which means they cannot utilise the latest, more efficient turbine models.
"Unclear regulatory frameworks and delays in legislation exacerbate investors' uncertainty," the groups warned.
The letter was signed by the heads of WindEurope, SolarPower Europe, BioEnergy Europe, the European Geothermal Energy Council, the European Solar Thermal Electricity Association, Ocean Energy Europe, Solar Heat Europe and the European Renewable Energy Federation.
It was addressed to five EC policymakers, including the vice-president for the European Green Deal, Frans Timmermans, and energy commissioner Kadri Simson.