Environment Agency staff have been abused by members of the public, in a development the body has blamed on politicians such as Eric Pickles
Workers from the agency are not being sent to flood-hit Wraysbury in Berkshire as a result, and have been told to report any incidents.
Justin Bowden, national officer of the GMB union commented: "This report of hostility from the residents on the Thames is a direct result of the irresponsible attack by Eric Pickles (Communities Secretary) and others on the EA.
"His incitement has led to the very people on the frontline who are actually helping to alleviate the situation bearing the brunt of people's frustrations.
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"For more than seven weeks since Christmas the Environment Agency's staff have been run ragged helping and supporting the victims of flooding. GMB members have been working double and triple shifts around the clock to protect and assist."
The GMB said David Cameron had repeatedly refused to say whether he would halt planned redundancies at the EA when he was asked by Labour leader Ed Miliband at Prime Minister's Questions.
Grants to the EA have been cut in real terms by more than a quarter over the past three years, said the GMB.
"The Government must immediately reverse the ludicrous cut of 1,700 EA jobs, followed by an independent inquiry into what are the realistic funding levels necessary to ensure the EA has both the capital budget to protect the country from flooding and drought and a big enough revenue budget to maintain, service and run these vital defences," added Mr Bowden.