He says he knows of one such case, where a corporate sponsor transferred to the tsunami appeal some money it had pledged to another overseas aid project.
The MP wants other charities that have been adversely affected by fickle corporate support to get in touch with him so that he can bring their case to the House of Commons, perhaps in the form of an early day motion.
He said that companies that have benefited from publicity by pledging money to the tsunami must not do it at the expense of the support they promised to other charitable causes.
"The public could be misled by the fact that money pledged by some companies is actually recycled money," he said.
Harris has written to 25 companies in the UK to ensure that the money they have pledged to the tsunami appeal is new money.
Harris can be contacted at email@example.com.