By Andrew Firestone

State officials denied a contract extension for Green Line work last week to a firm that once worked on Boston’s bloated Big Dig project.

“Given the substantial increase in contract value represented by this amendment, the board believed it was prudent and responsible on behalf of taxpayers to re-bid this contract,” said MBTA spokesperson Joe Pesaturo.

The cost of the long delayed extension has increased from $438 million in 2007 to a current estimate of $954 million.

The refusal of the Board to ratify the $24.5 million contract extension is another in a long history of delays to the project.

In 1990, state officials promised Somerville residents they would complete a Green Line extension through the city and into Medford as a way to offset air pollution caused by the Big Dig. In 2005, the Conservation Law Foundation (CLF) sued the state because it had not taken the necessary steps to complete the project on time. In November 2006, CLF and the state settled and agreed on a binding commitment to complete the project by 2011. That commitment was initially pushed back to 2014 and again to 2015.

Last month, state transit board member Liz Levin was forced to recuse herself from the vote after discovering her past affiliation with Parsons Brinckerhoff last month.

While saying the amendment was not unusual, Pesaturo did say that the board was “not comfortable” with this particular amendment and preferred a re-bid.

“[Secretary of Transportation Jeffrey] Mullan made it very clear to the DOT planning staff that he wants this re-bid process expedited. He wants them to come back to him with an action plan and he wants to see this done as quickly as possible.”