Former Queensland Nickel workers are being told to sign a document gagging them from making any disparaging comments about Clive Palmer in exchange for receiving their outstanding entitlements.

Palmer, whose United Australia party is running candidates across the country in Saturday’s federal election, announced last month he would pay entitlements to hundreds of workers who lost their jobs when his Townsville nickel refinery went bust three years ago.

When the company collapsed in 2016, it owed about $300m to creditors, including local businesses and the federal government, which covered the entitlements of many workers. It is estimated workers are still owed about $7m.

Palmer has established a trust, administered by Brisbane-based lawyer Sam Iskander, who told AAP this week that about 20 claims had been paid.

Guardian Australia has seen a copy of “deed of release” documents, prepared by Iskander’s firm, Alexander Law, which former employees are being asked to sign in order to be paid.

The documents include a clause that the workers “shall not make any disparaging comments in relation to … Clive Frederick Palmer and all related companies and entities”.

Workers are also asked to agree to a condition that they release Palmer and his companies from any legal action arising out of their employment with Queensland Nickel.

Giri Sivaraman, an employment lawyer from Maurice Blackburn acting on behalf of unionised former QN workers, told Guardian Australia some had been desperate for the money and had signed the agreement.

“Some of them are very concerned about giving up their rights,” he said.

Sivaraman said the clauses asked workers to waive their rights in order to be paid money to which they had been entitled for three years. Those rights included making comments about a prominent candidate at the federal election.

“They’ve got to agree to a complete gag,” Sivaraman said. “As a matter of law you shouldn’t have to give away your rights to engage in political debate.”

Guardian Australia has contacted Iskander, who is administering the trust and is responsible for assessing claims and processing payments, several times since Tuesday morning. He has not returned calls.

After a years-long advertising blitz, Palmer’s United Australia party will have an influence on Saturday’s election result, particularly in Queensland seats where the preference flows from minor parties will be critical.

In the Townsville seat of Herbert, where most of the former QN workers still live, polling has shown the UAP with between 7% and 14% of the primary vote. The candidate in the ultra-marginal seat, former rugby league player Greg Dowling, is directing preferences to the Liberal National party.