The militant national construction union faces fines of close to $1 million for disrupting work sites in NSW and Queensland, and allegedly inciting workers to wear shorts, defying safety rules.

The penalty judgments come in the wake of the Fair Work Commission's approval of a merger between the Construction, Forestry, Mining and Energy Union and the Maritime Union of Australia, with a total 144,000 members, combined revenue of $146 million a year and $310 million in assets.

The CFMEU and 19 officials were fined $817,500 after they shut down two major Brisbane worksites as part of a campaign allegedly aimed at forcing a company to sign the union's enterprise agreement.

The union and one of its officials were also fined $58,500 after allegedly inciting workers to wear shorts on a building site in Newcastle.

The Australian Building and Construction Commission (ABCC) took legal action against the CFMEU after it encouraged workers to wear shorts and short-sleeved shirts in defiance of construction company John Holland's safety policy, which required long sleeves and long pants to be worn.