The Committee on Standards in Public Life is rewriting its guidelines on potential conflicts of interests.
It wants to know what the "reasonable limits" should be and whether they should be different for ministers and backbench MPs.
It comes after controversy over George Osborne's jobs in banking, public speaking and journalism.
The Conservative MP for Tatton, in Cheshire, will take up his new role as editor of the London Evening Standard on 2 May, according to sources at the newspaper.
Within 24 hours he will head off to Paris to address hedge fund managers and investors, according to the Press Association.
Standards committee chairman Lord Bew said: "We welcome views from the public and any interested parties on these issues.
"For example, what factors should be taken into account in determining the 'reasonable limits' on MPs' outside interests and is the current level of transparency sufficient?"
The consultation will run until Friday, 28 April.
The committee's findings of the review will be reported to the Commons Committee on Standards' review of the Code of Conduct for MPs in June.

Tuesday's 3-2 victory at Plymouth Argyle ended an eight-game winless run and means the O's are only in the drop zone on goal difference.
"I've got to keep the boys grounded but I've let them be happy because they deserve it," he told BBC Radio London.
"I won't get carried away if we win as we're still second from bottom."
Webb, 33, is the youngest manager in the English Football League and became Orient's fourth boss of the season on 29 January.
The former Southend and Hull striker has been forced to rely on young players, with 10 of the squad at Home Park being products of the east London club's academy.
After ending a six-game losing streak in his third game in charge against Yeovil on Saturday, late goals from Gavin Massey and Sandro Semedo gave Orient their first victory since beating Crawley on Boxing Day.
"I'm new to management but I have confidence in my own ability and I know how to set up a team," Webb added.
"I know what the young players can bring; heart, passion and all the things the supporters want to see.
"It's been a long time since we've been happy after a game but we have a long way to go. There is no point in everyone saying we are playing well and have team spirit if it is only for four games."
However, the win at Plymouth has been marred by Argyle reporting O's skipper Liam Kelly to the Football Association for an alleged shove on a ball boy.
Meanwhile, defender Nicky Hunt picked up his 10th caution of the season and will miss Saturday's visit of fellow strugglers Notts County, who are managed by former O's player-manager Kevin Nolan.
An ethics watchdog want to know what the public thinks about MPs having second jobs.
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Leyton Orient boss Danny Webb wants his squad to remain focused in their League Two relegation battle after recording their first win of 2017.