Former Australian Workers Union official Robert Kernohan claims Opposition leader Bill Shorten warned him against blowing the whistle on the union's slush fund scandal because it would threaten his future in politics.

In a sworn statement to the royal commission into trade unions, Mr Kernohan who was president of the Victorian branch of the union at the time, said Mr Shorten told him in 1996 to ''think of your future''.

"He said, 'If you pursue this, a lot of good people will get hurt and you will be on your own. Look Bob, you've been lined up to take a safe Labor seat of Melton in the Victorian Parliament," Mr Kernohan said in his statement.

A spokesman for Mr Shorten said: "As Mr Shorten has said repeatedly, these claims are completely untrue.