A meeting is scheduled for next week between George Brumwell, general secretary of UCATT, Ed Balls, the Treasury's chief economic adviser, and John Monks, general secretary of the TUC.
Minister for transport John Spellar has also agreed to a separate meeting with UCATT to discuss direct employment.
The move comes in the same week that the Strategic Rail Authority launched its plan to revitalise the nation's rail network.
Brumwell said he would argue that all government contracts should contain a clause requiring contractors to use only directly employed staff. He is beginning with rail contracts because a large number of them are likely to be let in the next year.
He said: "The main argument centres on the need to implement a directly employed workforce on government transport contracts to help solve the problems of the nation's network. This move would help to complete the amount of work to be carried out in the rail sector in the near future."
He said he would present Balls with the findings of a UCATT report into bogus self-employment. This found that the practice was rife, and advanced the economic case for direct employment.
Last November, a UCATT report entitled Undermining Construction accused the Inland Revenue of sanctioning a deal with concrete contractors that permitted bogus self-employment.
The report claimed that concrete group Construct and the Inland Revenue has agreed to wrongly classifying a large number of directly employed workers as self-employed. The union said contractors preferred this sort of arrangement as it cost less in tax and National Insurance.
A Treasury spokesperson confirmed that Balls was due to meet Monks and Brumwell but refused to be drawn on the meeting's agenda.
He said: "We totally agree with the Inland Revenue's standpoint that bogus self-employment would never knowingly be sanctioned."