Parliament's dual citizenship drama threatens to widen further after the Turnbull government made it clear its disclosure regime will include marriage.

The original version of the disclosure regime - agreed to by the government and opposition earlier this month - focused on citizenship by birth and descent. It would have required MPs to disclose details relating to their birthplace, parents and grandparents, but not necessarily spouses.

But the government has now confirmed MPs will be required to disclose relevant details relating to marriage.

Dozens of nations grant citizenship by marriage - or have done so in the recent past - and in a number of them the conferral is automatic.