UPDATE: Union chiefs John Setka and Shaun Reardon may face up to 15 years in jail after being charged with blackmailing concrete company Boral in the most significant development to emerge from the royal commission hearings into union corruption.

The criminal charging of the Construction, Forestry, Mining and Energy Union heavyweights will place intense pressure on Victorian Premier Daniel Andrews and federal Opposition Leader Bill Shorten as the ALP has strong ties to the CFMEU.

Mr Andrews has been under pressure to sever the party's ties with the union in light of the commission's findings after several court judgments highlighted the union's disregard for the law. Mr Shorten will announce on Monday Labor's reforms to deter corruption in unions.

The CFMEU has donated millions of dollars nationally to the ALP in recent years. The union donated $400,000 to the Victorian Labor Party alone from 2012-14.