The Labour MP Jack Dromey was today found to have breached Commons rules after he failed to register almost £30,000 in payments from the Unite trade union.
The Commons Standards and Privileges Committee described the failure to declare the "significant payments and benefits" he received for his work for the union in the register of members' interests as "serious".
In his entry in the register in June 2010, Mr Dromey, who was Unite's deputy general secretary, said he was giving up the post and had declined his salary following his election as MP for Birmingham Erdington in the May general election.
However the Parliamentary commissioner for standards John Lyon found he had continued to work 10 to 15 hours a week for the union until the end of October 2010, for which he received £28,000, which he failed to declare when he updated his entry in the register.
"We consider Mr Dromey's failure to ensure that the register gave an accurate picture of his relationship with Unite is serious," the committee said.
The committee said if he had not been a new MP at the time they would have considered ordering him to make a personal statement on the floor of the Commons to apologise.
However it accepted he had offered an immediate apology for the breach and cooperated fully with the inquiry and said it would accept his offer to apologise in the chamber through a more low-key point of order.
Making his personal statement to the Commons, Mr Dromey said: "I would like to make an apology to the House.
"A report has been published by the Standards and Privileges Committee following an investigation by the Parliamentary Commissioner for Standards.
"I failed to update in time my initial registration in respect of payments received from my previous employer during the months of June to October 2010. This I have now done.
"I also failed to declare an interest in speaking in two debates on June 16, 2010 and September 16, 2010.
"Notwithstanding that the commissioner and the committee noted that the breaches were unintentional, I want to apologise unreservedly to the House and I will in future fully abide by the rules of the House."
Conservative MP Andrew Bridgen, who complained to the Parliamentary Commissioner for Standards about Mr Dromey's failure to register union payments, said: "It is right that Jack Dromey's serious misconduct has been investigated and condemned. As a former Labour Party treasurer and with his wife, deputy Labour leader Harriet Harman, having been an MP since 1983, he should have known he needed to register his union payments.
"Once again, Labour have been found guilty of putting the vested interest of the trade unions ahead of the interest of the British people.
"Ed Miliband can talk all he likes about taking on the unions, but unless he publicly reprimands his shadow minister's misconduct, people will see him for what he is - weak and in the pockets of his union paymasters."