MSPs have expressed concern that Scottish government plans to provide more information about the lobbying of politicians do not go far enough.
Organisations and individuals would have to register following the face-to-face lobbying of MSPs or ministers.
But a majority on Holyrood's standards committee said vital information could go unregistered.
MSPs on the cross-party committee said ministers should consider including all forms of communication.
The committee, which in principle endorsed the government's plans, contained in the Lobbying Bill, also recommended the Scottish government consider broadening the definition of regulated lobbying to include communications with public officials other than ministers and MSPs.
The Scottish government welcomed the committee's endorsement, and said would look carefully at its recommendations.
Lobbyists work for companies, charities and other groups to influence political decisions through their contacts.
It is seen as legitimate and valuable activity, but the Scottish government said the activity needed to be more transparent.
Publishing a report on on the Lobbying Bill, Standards committee convener and SNP MSP Stewart Stevenson, said: "The committee understands that the definition of lobbying was restricted to oral communication in order to focus the scope of information to be captured and to produce a low burden, light touch regime.
"Nevertheless, the majority view is that restricting registration to oral communications is an artificial distinction which could leave a great deal of information unregistered.
"We recommend that the government reviews the potential impact of altering its definition to include communications of any kind, with a view to establishing what amendments to the bill might be necessary."
Welcoming the committee's report, the Scottish government's minister for parliament, Joe Fitzpatrick, said: "The Scottish Parliament already has strict rules over lobbying, but it is important to ensure that such activity is conducted openly.
"We will carefully review the recommendations with a view to ensuring that the proposed register remains proportionate, simple and does not place an undue burden on organisations."
The Lobbying Bill would need to be approved by a vote of parliament before becoming law.
The only lobbying row to have hit the Scottish Parliament came in 1999, when the Observer newspaper claimed public relations firm Beattie Media touted for business by offering privileged access to Scottish ministers, including future first minister Jack McConnell, who held the finance brief at the time.
The company denied the allegations and the standards committee later cleared McConnell of acting improperly - but voiced concern over an apparent conflict in evidence given by his constituency secretary, Christina Marshall, and lobbyist Alex Barr.