Former Siptu official Matt Merrigan is understood to have written to the Dáil Public Accounts Committee, questioning its authority to compel him to appear before it as part of an investigation into a highly controversial €4 million fund.

In a letter to the committee, Mr Merrigan maintained that a Garda investigation into the controversy was still open. The committee is expected to seek legal advice on the issue.

Earlier this year, the committee won the right to compel Mr Merrigan to appear after he had declined to give evidence before it.

The committee wants to ask Mr Merrigan about the operation of a bank account – described as a slush fund – which was used to pay for foreign travel by civil and public servants as well as union officials.

A report by the Comptroller and Auditor General found that more than €4 million in funding from a variety of State bodies, mainly in the health sector, was paid into an account known as the Siptu national health and local authority levy fund.

This account was established in 1998 by Mr Merrigan and Jack Kelly, a member of Siptu's national executive.