Morale among Forth Road Bridge staff is "extremely low" amid concerns about job cuts when tolls are abolished, MSPs have been told.
The bill would scrap tolls on the Forth and Tay bridges
Sandy Smart, of the Transport and General Workers Union, also said he had been refused a ministerial meeting over an issue which was "up in the air".
Meanwhile, Forth bridge master Alastair Andrew urged parliament to provide a precise timescale on the toll removal.
A bill to scrap charges on the Forth and Tay bridges has been published.
The SNP made ending tolls a pledge during May's election campaign.
A Scottish Government spokeswoman said it appreciated the decision to abolish bridge tolls created uncertainty for the workforce, but added that the responsibility for staff involved rested with the bridge authorities.
Mr Smart told the Scottish Parliament's transport committee that there had been no government consultation over the issue and that a request for a meeting with Transport Minister Stewart Stevenson was refused in a "very curt" letter from his secretary.
"Morale on the bridge among the staff is extremely low," he told the committee.
"The staff involved in collection of tolls and involved in the admin side are more or less resigned to the fact that a lot of them will end up losing their jobs."
Mr Smart added: "At the moment, people don't know if they're going to be in a job at Christmas. It's really quite unsatisfactory."
He also raised concern about the eroding of staff conditions if the operation was privatised in the future, in a similar way to trunk road maintenance, but admitted under questioning from Nationalist MSP Rob Gibson that his comments were speculation.
STUC assistant secretary Stephen Boyd told MSPs that a ministerial meeting would put staff at ease and stop "unhelpful" speculation.
Alastair Andrew, Forth Road Bridge general manager and bridgemaster,
said he expected between 35 and 40 job losses from the current staff of 104.
Giving evidence on the tolls abolition bill, Mr Andrew said his two overriding concerns were the safe maintenance and operation of the Forth Road Bridge and the welfare of staff, "many of whom have served over many years and for whom this legislation is life-changing".
He added: "I would urge parliament to seek clarity on the precise timing of the tolls being removed.
"This is vital if we are to plan effectively and implement the required remodelling works ... and the communication process for those staff whose jobs will be affected."
The government spokeswoman said: "We are aware that the bridge boards are working with staff and the trades unions to examine all opportunities for redeployment of staff, or possible voluntary early retirement or redundancy arrangements.
"Ministers are committed to ensuring that staff are treated with fairness, dignity and respect throughout the process."
It is understood the tolls project will cost up to £16m per year to implement, plus a similar amount to pay off the existing debt on the Tay Bridge.
The bill has the support of all parties, except the Greens and environmentalists claim scrapping the tolls will lead to at least 20% more traffic.