Mr Tinkler’s $50,000 in donations to the NSW Nationals have already been questioned because of his stake in property development company Buildev, despite developers being prohibited from donating to political parties.

Mr Tinkler founded Aston Resources in 2008, publicly listed in mid 2010, and was appointed board chairman in November last year as well as being a substantial shareholder.

In a project application dated August 2010, Aston declared it had made no political donations.

Under planning assessment laws, a proponent has to declare to the Planning Department political donations made within two years of an application, including those made by its directors.

It is also required to disclose within seven days any subsequent donations.

Mr Tinkler gave $5000 to the party’s state campaign and $45,000 to its federal campaign at a fund-raiser on March 31, according to NSW election funding declarations made public in November.

A Department of Planning and Infrastructure spokeswoman said yesterday it had contacted Aston in November and ‘‘was again advised that there was nothing to declare’’.

‘‘The department is investigating the matter,’’ she said.

‘‘If the company is found to have breached its obligations under the Environment Planning and Assessment Act, the department will decide what further action to take.’’

Aston Resources acting chief financial officer Garry Wayling said yesterday the company would clarify its obligations in relation to Mr Tinkler’s donations and ensure it acted appropriately.

Greens MP Jeremy Buckingham said there were ‘‘serious questions’’about whether proper declarations had been made.

‘‘The public should be aware that Nathan Tinkler has given a huge amount of money to the Nationals, while the government is making a decision on whether to approve his coalmine,’’ Mr Buckingham said.

Mr Tinkler has previously said he made the donations in good faith and denied any intentional breach of donations laws.

A spokeswoman for Planning Minister Brad Hazzard said the application was to be referred to the independent Planning Assessment Commission because of the donations and the substantial number of public objections to the project.

A NSW Election Funding Authority spokesman said it was continuing to audit all 2010-2011 declarations and was not specifically examining Mr Tinkler’s donations at present. The NSW Nationals said the party was awaiting advice from the authority.