People who sign up to prevent marketing "cold calls" are being encouraged to complain if they are telephoned by political parties.
All the parties are using call centres
The Lib Dems claim the Tories and Labour are exposing themselves to fines of up to £5,000 through election calls.
The Lib Dems have written to thousands of people encouraging them to complain.
Labour and the Tories say they are sticking to the rules, which do not prevent telephoning people about voting intentions.
Telephone call centres are expected to be used as never before by all the three major parties in the run-up to the general election.
But seven million telephone numbers are on the Telephone Preference Service (TPS) lists, which ban unsolicited sales and marketing calls.
The Lib Dems are setting up a new website to encourage voters to register formal complaints when they receive "nuisance calls" from Labour or the Tories.
Lib Dem president Simon Hughes said: "Members of the public register with the Telephone Preference Service because they don't want to be called at home.
"Conservatives and Labour are now improperly pestering voters by telephoning them against their will."
He said his party had removed TPS users from its phone lists.
"We demand that the Labour and Conservative parties now demonstrate that they are not breaking the spirit or the letter of the law by using information for any campaigning purposes if they call TPS-registered consumers," he added.
The Lib Dems are writing to thousands of people on the TPS telling them how to complain.
That move was labelled a "political stunt" by a Labour source.
The source added: "If they were serious about not disturbing people on the TPS, they would not be sending them junk mail either."
The Lib Dems have yet to receive a formal reply from the information commissioner to their complaint about the cold call.
But last week a Labour spokesman said "voter identification" calls were allowed under the TPS rules.
"When we ask which party they will vote for, that is not marketing and we have very clear legal advice that it is not," said the spokesman.
"So it is not covered by the Telephone Preference Service."
He said the party always asked people if they would be happy to be contacted again and if they said no, they were not rung again.
'Depends on script'
A Conservative spokeswoman said the party stuck to the rules when it rang TPS users.
She said: "We do apply TPS but in line with the law. We would not do things that are not allowed in the law."
Assistant information commissioner Phil Jones said it was classed as marketing if political parties telephoned people to encourage them to vote for them.
But "classic market research", such as a poll of voter intentions, did not constitute direct marketing, he said.
"If a party rings a person who is registered on TPS to ask about their voting intention and goes on to encourage that voter to support them, the party may well be in breach of the regulations," said Mr Jones.
"In summary, whether a party calling TPS registered voters to check their voting intentions will breach regulations will depend on the script used and whether the script is followed."
Mr Jones said the watchdog received "very few complaints" on the issue.