Labor has accused the government of “stacking” the industrial umpire after it appointed six people to senior positions, most from employer backgrounds.

On Friday, the industrial relations minister, Kelly O’Dwyer, announced six new deputy presidents of the Fair Work Commission and one new commissioner, which Labor leader Bill Shorten said has brought its tally to 20 employer appointments in a row.

The commission has wide-ranging powers, including setting the minimum wage, penalty rates, dealing with bargaining disputes and deciding cases of unfair dismissal.

Union and employer groups have a long history of accusing unfriendly governments of stacking the commission.

Of the new deputy presidents, four have worked directly for employer associations, including Amanda Mansini, the director of workplace relations at the Australian Mines and Metals Association (Amma), and Gerard Boyce, a barrister who has worked for both Amma and the National Electrical and Contractors Association.

Bryce Cross, a barrister who was formerly the head solicitor at the Chamber of Manufactures of NSW, and Janine Young, a partner at law firm Corrs Chamber Westgarth since 2011, were also appointed deputy president.

The government promoted Tony Saunders, a commissioner it appointed in 2015, to deputy president and also appointed Nicholas Lake, a senior human resources manager at corporates BHP Billiton, ExxonMobil, ANZ and Philip Morris, to the senior position.

Fair Work Commission deputy presidents are paid $460,000 a year and generally sit on the most significant cases.

According to the Australian, the Fair Work Commission president, Iain Ross, recommended only one new appointment but O’Dwyer said she made the seven appointments after many parties urged her to give the commission extra resources.

On Friday, Shorten accused the government of “institutional stacking” and “crass conduct” because it is in a panic to make appointments before the 2019 federal election.

“They’ve actually appointed to this independent umpire 20 people in a row with employer backgrounds,” he told reporters in Canberra. “They are tainting the commission, they are stacking it with mates.”

“I don’t think that there was a big jobs vacancy for deputy presidents of the Fair Work Commission.”

O’Dwyer said the appointments will give the industrial umpire “the ability to approve pay increases and better working conditions more quickly for Australian workers”.

“This group of appointees is highly qualified and well regarded in their respective professions,” she said. “I am confident the appointees will bring comprehensive expertise and valuable skills to the Fair Work Commission.”

When Shorten was workplace relations minister he made two appointments to the position of vice-president, effectively demoting other senior tribunal members, in a move that infuriated employer groups.

In 2016, Amma accused Labor of hypocrisy over claims of tribunal-stacking, because Labor made 18 appointments from employee or trade union backgrounds out of a total of 26 appointments in its six years in government.

In 2018, the Fair Work Commission increased the minimum wage by 3.5%. In recent decisions it has caused consternation among both employers – who dispute the conclusion that “modest and regular” minimum wage rises do not add to unemployment – and unions, who argue the minimum has not kept up with median wages.

In February 2017, the commission ordered a cut to Sunday and public holiday penalty rates in the retail, pharmacy, fast food and hospitality industries, prompting Labor and the Greens to promise to reverse cuts.