The movement of seven trams from the Luas red line to the green line has been labelled "robbing Peter to pay Paul" by the Green Party.
Dublin south central representative Ed Davitt has described the movement of the trams as an "indictment of poor planning" during the transition to the Luas Cross City.
It is understood that the move by the National Transport Authority (NTA) along with Transport Infrastructure Ireland has been undertaken in what has been described as an "all hands on deck" effort.
A transport source told the Herald that the decision was made in order to ensure that the Luas lines were operating as efficiently as possible.
The revelation came following a parliamentary question to Transport Minister Shane Ross by the Green Party's Catherine Martin, who said the situation with overcrowding is "becoming dangerous" and added the movement of the trams was a result of bad planning.
Her colleague Mr Davitt said it was "not a solution".
"It is completely unacceptable that red line commuters should suffer lower capacity and a less reliable service due to the poor planning for the rollout of the Cross City service," Mr Davitt said.
"The solution to alleviating problems on the green line is to create problems on the red line? That's not a solution - that's robbing Peter to pay Paul. Commuters, on the red line and on the green line, deserve better than this.
"The Government and the NTA must get on top of this issue, and quickly."
However, a transport source insisted that the movement of the trams has no effect on tram services on the red line and that all trams continue to arrive at their scheduled time.
The source added that the shift from red line to green line had been undertaken in order to ensure each tram is "best utilised".
It all comes as the Luas Cross City - which launched in December - continues to cause major disruption, particularly around the College Green part of the city.
Seven longer trams were purchased by Luas Cross City to alleviate the demand by commuters.
However, "an unforeseen technical fault" arose with two of the trams.
Mr Ross said all of the 55-metre trams will be put into use between now and May.