@David, yes, it would definitely be useful for the readers to know financial benefits gained by the authors in the course of their work. 

I agree with Michael. The reader should know what funding sources are

Appologies... here is the link to the article.

http://dailycaller.com/2015/02/27/what-does-a-conflict-of-interest-in-climate-science-look-like/

This is a reasonable question.

Although I agree with @Michael Brückner and @Zaida Chinchilla-Rodríguez, I suggest that making disclosure of funding sources for the research leading to publications is both not enforceable and probably not desirable.   Instead, it would be better to leave such disclosures as an option for authors.

This issue becomes quite complicated, if we consider funding sources for processing charges for open source articles.    See, for example,

https://www.researchgate.net/publication/272180349_The_'total_cost_of_publication'_in_a_hybrid_open-access_environment_Institutional_approaches_to_funding_journal_article-processing_charges_in_combination_with_subscriptions

See, also:

https://www.researchgate.net/publication/232736822_Adherence_to_ethical_standards_in_publishing_scientific_articles_A_statement_from_the_International_Journal_of_Cardiology

Article The ‘total cost of publication’ in a hybrid open-access envi...

Article Adherence to ethical standards in publishing scientific arti...

Thank you all for your contributions. James' argument for making it optional makes sense - one should not enforce it, but ask authors to volunteer such information. 

I think researchers will disclose this to show they have nothing to hide. This, of course, does not imply those who don't are hiding something.

I think that it is best practice to disclose the funding source of research as well as to declare that there has been no conflict of interest with it. Some journals even ask and publish it along the paper.