Union approval is needed to formally introduce the grade.
Corby said the union was aware that several large M&E contractors were planning to trial the grade and has warned union officials to be vigilant on the issue.
He said: "We see the multiskilling grade as deskilling and we cannot accept that approved electricians are undermined in this way."
Corby has written to all of his construction officers to warn them of allegations that cabling contractors are encroaching on approved electricians' work.
The contractors are trialing the new grade for a group jointly run by the Heating and Ventilating Contractors Association and the Electrical Contractors Association.
We cannot accept that approved electricians are undermined in this way
Paul Corby, national officer, AMICUS-AEEU
One of the firms set to trial the grade is Shepherd Engineering Services. An internal Shepherd memo, seen by Building, revealed that training body ESTTL is piloting the trials with SES.
The memo said Shepherd Engineering Services managing director Allan McDougall had called for 15 employees to review the grade.
A statement from SES said: "We, along with several other M&E contractors, were asked by ESTTL to review a document on the multiskilling grade." The HVCA refused to comment on the scheme and the ECA was unavailable.
Unions see the introduction of the multiskilling NVQ as an attempt by employers to resurrect the controversial "skilled mechanical assembler" grade, after the union defeated it in 1997.