The two companies said they had agreed to halt future windfarm projects because the government had failed to provide "reliable framework conditions" for wind power development.
"We will not make any new public tenders for building windfarms, but will focus on finishing existing projects for the time being," a Tennet spokeswoman told the newspaper "Weser-Kurier" on Thursday.
Grid operator Tennet is responsible for connecting German offshore windfarms to the national power grid, and runs several wind power projects together with RWE.
Hans Bünting, RWE's financial officer, told the same newspaper that such projects lacked the "necessary legislation, including regulation governing delays in connecting projects to the power grid."
Bünting added that RWE was not going to develop new windfarms "until these issues have been sorted out."
In a surprise change of its energy policy, the government decided last year to phase out nuclear power by 2020, while at the same time raising the amount of renewable forms of energy from currently 20 percent to 35 percent.
However, there has been mounting criticism from German utilities, complaining that the sharply increased use of renewable energy, notably offshore wind power, has made it impossible to transport the electricity to consumers due to bottlenecks in the national grid.
Last week, German utility E.ON complained about "huge delays" in connecting windfarms to the grid.
"Nobody is going to invest in wind power anymore, if grid connection remains unstable," Mike Winkel, head of E.ON's Climate & Renewables unit said in an interview for the "Berliner Zeitung" newspaper. The company's Amrumbank offshore windfarm, for example, currently faces a "delay of 15 months," he added.
Germany's Federal Cartel Office also expressed doubts about current energy policy, saying in a recent report that "several windfarms must be connected every year" in order to meet the governments goal of 35 percent of renewable energy by 2020.
The government has admitted that there are problems, saying that the power grid needed to be completely reconstructed in order to transport electricity from the wind-rich north of Germany to industrial zones in the south. However, grid development, the government said, was often inhibited by public resistance because people were opposed to overhead transmission lines in their neighborhoods.