Blogger Guido Fawkes claims up to 17 Labour candidates, including Mr Matheson, failed to declare spending on the vehicles used during last year’s general election campaign.
Operated by Labour Students, the buses targeted marginal seats including four where Labour won such as the City of Chester constituency and Wirral West.
The news comes after it emerged in May that Cheshire Police were investigating allegations the Conservative Party breached election expenses rules concerning its 2015 general election ‘battle bus’ that visited Chester and also the Weaver Vale constituency, where Graham Evans was elected as the Tory MP.
At the centre of allegations against both political parties is whether the expenses should have been declared as local or national expenditure. Both parties insist the spend should count as national spend and that local candidates did not have a responsibility to declare any expenses.
An Electoral Commission spokeswoman told The Chronicle: “Our guidance explains that candidates need to make an honest assessment as to whether an expense was for their election or whether it was for promoting the national party.
“If an expense is within a constituency and only promotes the national party and national policies then that should count as national party spend. If it promotes both the local candidate and national policies, then a portion of the cost should be allocated towards the candidate’s spending limit and a portion towards the party’s national spending limit."
She added: “Any allegations regarding the spending returns submitted by candidates at the general election are for the relevant local police force to respond to.”
Cheshire Police spokeswoman Rachel Hayes said: “We are reviewing all reports made to the police about both Conservative and Labour parties in conjunction with the Electoral Commission.”
She confirmed a number of letters had been received bringing the issue to the attention of the constabulary in both cases.
Guido Fawkes wrote on his blog about the latest allegations against Labour: “New MPs including Cat Smith (Lancaster and Fleetwood), Margaret Greenwood (Wirral West) and Chris Matheson (Chester) did not declare these transport costs, despite benefiting directly from campaigners bussed into their constituencies.”
Chester MP Mr Matheson, who was elected with a miniscule 93-vote majority, declined to comment but referred The Chronicle to the Labour Party North West regional office.
A Labour spokesperson said: “This was part of a nationally branded tour so the transport costs are rightly national spend. Labour’s spending is within the law and the rules set out by the Electoral Commission.”