John Howard has questioned the Coalition’s decision to launch two royal commissions in its first year in government, saying that the process shouldn’t be used for “narrow targeted political purposes”.

A royal commission into the home insulation scheme has already concluded, while another royal commission, into unions, is underway.

Howard told the Australian: “I’m uneasy about the idea of having royal commissions or inquiries into essentially a political decision on which the public has already delivered a verdict.

“I don’t think you should ever begin to go down the American path of using the law for narrow targeted political purposes. I think the special prosecutions in the US are appalling.”

Four young men died during work provided by the home insulation scheme in 2009 and 2010. The previous Labor government introduced the scheme as a way to stimulate the economy during the global financial crisis.

The home insulation royal commission cost about $25m and followed several previous coronial and Senate inquiries into the matter. The commission questioned former prime minister Kevin Rudd about the scheme’s roll-out, with the subsequent report finding that the program was seriously flawed.

“I am uneasy about those approaches,” Howard said. “I have to say I’m not happy about that but that’s a decision the government makes and, after all, the former government was tipped out on the strength of, among other things, the failure of the home insulation scheme. There has been coronial investigations.”

Howard is the latest former prime minister to question how the Coalition is handling the royal commission process. Earlier this year, Malcolm Fraser and Bob Hawke expressed concern that the government would break a long-standing convention of cabinet confidentiality by handing certain documents over to the home insulation royal commission.

Last week, Julia Gillard, yet another previous prime minister, gave evidence at the royal commission into trade union governance and corruption. Gillard was questioned at length about regularly repeated allegations that she used money from a union slush fund to make renovations to her home in the 1990s.

Labor has accused the government of using the royal commissions as part of an ideological witch-hunt against the previous administration. Mark Dreyfus, the shadow attorney general, told Guardian Australia that Howard’s view on the use of royal commissions is telling.

“Establishing legal inquiries for political purposes is an abuse of power,” he said. “Royal commissions serve our community well – the child abuse royal commission is a good example of that. But we have had two inquiries set up for primarily political purposes.

“The union commission is very much a pursuit of a political vendetta. My concern about the home insulation royal commission is that millions of dollars was spent investigating something that has already been investigated eight times.

“I’ve been appalled by both. When you have a former prime minister criticising this kind of abuse of power, it would surely make the Abbott government think again before using a royal commission for political purposes.”

Dreyfus insisted that he had no intention of pursuing a similar strategy if Labor won the next election and he became attorney general again.

“I’ve received a lot of mail that says Labor should use royal commissions in this way,” he said. “I would hope no future Labor government would do so.”