The Bridgwater and District Trades Union Council reacted angrily to the sight of Mr Liddell-Grainger joining flood victims protesting outside the Environment Agency in Bridgwater last week.
A TUC spokesman said: “Mr Liddell-Grainger would be better off protesting against his own Government, which has helped to cause this devastation.
“How dare he focus the blame on Environment Agency workers, who have struggled to carry out their duties in the face of Government cuts?
“The Tories have slashed £800 million from the country's flood defence budget. Why doesn't Mr Liddell-Grainger protest about that?
“We fully support Environment Agency workers in their campaign to stop the cuts and call upon anyone concerned to write to their MP, or email via http//www.theyworkforyou.com/mp.”
The TUC said their local MP should be more focused on addressing the news that an appeal by Somerset County Council for more flood funding has been refused by the Government.
Mr Liddell-Grainger said: “I am not criticising workers at the EA, but the people at the top.
“It is unfair to blame EA workers for something they have no power over because that power lies with EA bosses.
“To make this into a political attack is ridiculous. This is not about political parties, it's about people. I just want to ensure my constituents are protected and I'm not going to stop until that is accomplished.
“I haven't seen any TUC members doing anything to help. We should be trying to help as a team.
“There is hope for Somerset. We have pledges from the PM and flooding is finally being taken seriously.”
A public meeting is being arranged in Bridgwater on February 27. For details contact secretary D Chapple on 01278-450562.