An immigration staff member, who spoke to the Herald on condition of anonymity, said it was "common practice" for immigration officials to work overseas on tourist visas on short-term working stints.
He said the agency had been made aware that an officer had worked at the New Zealand Education Fair in Sri Lanka on a tourist visa, and other officers had worked as visa processing officers in Vietnam on "incorrect visas".
The Department of Labour, which oversees immigration, says it was aware of these allegations, but investigations found they had "no substance".
The department also backed the decision to send the Bangkok-based officer to work in Singapore on a social visit pass, despite the republic's rules stating visitors "are not permitted to engage in any form of business, profession, occupation or paid employment".
"The staff member was sent to Singapore as part of the department's response to the crisis in Bangkok to assist with business continuity," a department spokesman said.
"In this case, the staff member obtained the visa on arrival in Singapore as it had not been possible to obtain a visa before leaving Bangkok due to the closure of the city centre because of the riots."
He said the department's normal process was to contact the relevant embassy to obtain the appropriate visa for a staff member who is required to work. "Managers are regularly reminded of their obligations to ensure that staff members have correct visas.
"In an emergency situation such as this, it might be necessary to obtain a visa upon arrival in the host country."
Immigration has 27 seconded employees offshore, comprising three regional managers, 15 branch managers, five immigration managers and three risk analysts.
The department says it is unaware of any staff working without appropriate visas.
