The three main parties at Westminster have all urged their MPs to declare any family members working for them.
Party leaders are calling for greater transparency over MPs' expenses
Tory leader David Cameron said he would ensure from 1 April his front bench registered family staff and would urge the rest of his MPs to do the same.
Lib Dem leader Nick Clegg said he had done the same, while Downing Street said Gordon Brown was asking for more transparency from Labour MPs.
It comes after a Tory MP was suspended by the Commons for overpaying his son.
Derek Conway, MP for Old Bexley and Sidcup, has already been censured for overpaying Freddie's parliamentary allowances and has apologised to MPs.
He has had his party's whip withdrawn and says he will not fight the next election.
MPs voted on Thursday to suspend Mr Conway for 10 days and ordered him to return £13,161 of the money.
Party leaders cannot force MPs to register expenses with the Commons authorities, but Mr Cameron said he had received assurances from all his frontbench team that they would do so.
He said: "I think there's a need for greater transparency or openness when it comes to MPs' pay and staff and expenses and allowances.
"As a first step I will be asking my front bench colleagues from April this year to register, in the members' register of interests, whether they do employ any family.
"It would be a good first step. We want to show that MPs do work hard for their constituents and make good use of money."
Mr Cameron revealed that "just over" 70 - out of a total of 193 - Tory MPs employed family members. He said the figure had come from a "ring-round" of most the party's MPs.
Mr Clegg said there were "about 12" Lib Dem MPs, out of 63, who employed family members.
He also called for the number of family members that MPs can employ in their offices to be limited to one - and said MPs should be forced to produce receipts for spending more than £50. The current limit is £250.
Mr Clegg told BBC News 24: "There's a huge challenge for Westminster to haul itself from the 19th century into the higher standards of transparency in the 21st century.
"Yesterday I published on my website all those people who work for me and I am urging all my colleagues in the Liberal Democrat parliamentary party to do the same."
Labour has not revealed how many of its 352 MPs employ family members but a party spokesman said Mr Brown had made clear he expected "transparency" in a meeting with Chief Whip Geoff Hoon on Thursday.
The spokesman added: "But the important thing is not just that the staff are registered and identified appropriately but that they are doing the job for which they are funded by the taxpayer.
"That's what Mr Cameron and his party have previously failed to recognise."
Visiting a school sports project in Shropshire, Mr Brown said that "there's got to be transparency in all these things, from every MP, not just a group of MPs".
He added: "What really matters is the public is assured that the money is actually going to people doing the job.
"The important thing is transparency, so people know what's happening."
Mr Brown is expected to meet Labour's parliamentary committee on Wednesday to discuss how to make MPs' spending more open.
At the moment there are no rules against employing relatives paid for out of an MPs' allowances, and there is no requirement for any such link to be declared.
Labour MPs Lynne Jones and David Taylor have tabled a Commons motion calling for a system of "independent assessment" in all appointments when a relative or a close friend of an MP applies for a post.
And Conservative Bob Spink has tabled a motion saying jobs at Westminster should be given to "the most appropriately qualified".
He said staff should be employed by Parliament itself, to "deliver greater visibility and accessibility" to the public and called for an end to "substantial" second jobs for MPs.
Meanwhile, the Scottish Parliament's standards watchdog has told Scottish Labour leader Wendy Alexander she was wrong to keep donations to her leadership campaign a secret.
Labour said Ms Alexander had been advised that gifts exceeding £520 should be declared in the register of interests.