Industrial Relations Minister Kelly O'Dwyer is expected to announce on Tuesday the government will aim to legislate the changes before the next federal election due in May.

A recent decision by the Fair Work Commission provided eligible award-reliant casual employees with a right to request to convert to full-time or part-time employment.

“If award-reliant employees have the right to make a request and it is subject to reasonable safeguards for employers, it is only fair that the same right is extended to other casuals who currently do not have the same right," Ms O'Dwyer said.

While the commission's decision affected 1.5 million workers, another 500,000 mining, retail and hospitality casuals are expected to be covered by the new laws.

Ms O'Dwyer will also move to allay concerns over a recent Federal Court decision which business groups argued opened the door to so-called "double-dipping" of entitlements.

The ruling found truck driver Paul Skene was entitled to an annual leave payout from labour-hire firm WorkPac despite being a casual employee because of his long-term regular pattern of work.

The new regulation will mean where an employer has paid a casual loading to an employee engaged as a casual, it may potentially be offset against any claim for National Employment Standards entitlements.

“Every employer must comply with their legal obligations, but being forced to pay for entitlements twice is unfair and potentially crippling for many small businesses," Ms O'Dwyer said.

The minister has intervened in a separate test case, with WorkPac seeking declarations a former employee, Robert Rossato, was a casual employee and not entitled to be paid leave entitlements.

The Australian Council of Trade Unions is also weighing an intervention, with secretary Sally McManus accusing Ms O'Dwyer of defending companies rorting the system.

The union movement has been targeting increased casualisation of work as one of the key planks of its ongoing Change The Rules campaign.

Australian Associated Press