Embattled Labor senator Sam Dastyari has gone to ground, cancelling an event in Sydney and maintaining an unusually low media profile as the government continues to pressure Bill Shorten to sack him from the shadow cabinet.

Attorney-General George Brandis has refused to rule out the possibility Senator Dastyari broke the law although it is unclear what rule would have been breached. He issued a challenge to Mr Shorten, asking whether he is willing to accept a senior colleague being "in the pay of a foreign-controlled entity".

Calls for reform of the political donations system have also strengthened as Greens leader Richard Di Natale, joined by conservative senator Cory Bernardi, propose allowing only people on the Australian electoral roll to donate to parties, halting contributions from companies, unions and foreign entities.

But Senator Brandis has rejected any immediate moves for reform, insisting there is no link between the broader system and the Dastyari imbroglio, which involved a private debt being paid by a Chinese-Australian donor and the senator's rogue support for China's position in the South China Sea dispute.