Nick Clegg was embroiled in a row on the eve of his final visit to the Oldham East and Saddleworth byelection amid allegations that the Liberal Democrats may have broken strict electoral rules.

As the deputy prime minister prepared to rally voters today, the cabinet secretary Sir Gus O'Donnell was asked to rule on whether the Lib Dems breached the ministerial code by promoting a government announcement during the campaign.

The row broke out after Andrew Stunell, the Lib Dem housing minister, announced after a visit to the constituency on Saturday that the government would be unveiling a £100m government scheme to bring empty houses back to use.

In a press release issued on Sunday night the Lib Dems said that Stunell had visited Oldham with the party's candidate, Elwyn Watkins, to "highlight the problem of empty homes in advance of new government proposals that would help bring some properties back into use". Stunell then outlined the plans in a formal government press release issued by the department for communities and local government today.

Labour tonight asked the cabinet secretary to rule on whether Stunell has breached Whitehall "purdah" rules which come into force during elections. These are designed to prevent a governing party using its privileged position in Whitehall to gain advantage during an election campaign.

In a letter to O'Donnell, the shadow cabinet office minister John Trickett raised a "possible breach of the ministerial code" after Stunell's press release. Trickett wrote: "The announcement was clearly made to influence the outcome of the byelection. This has the appearance of a clear breach of guidelines on the appropriate communication of government announcements.

"I know that you take your role as guardian of standards for government communications very seriously and that you will be very concerned if indeed there has been a breach. I am sure that you will wish immediately to instigate a review to determine the nature of the actions taken by the minister, and any involvement by the departmental civil servants. Can you please confirm that you will indeed conduct an enquiry?"

O'Donnell polices government announcements during elections. Strict rules apply during general elections when ministers are barred from making all but the most bland announcements. Government business is allowed to continue in the runup to byelections, though ministers are expected to refrain from using campaign visits to make policy announcements.

A Lib Dem spokesman said: "No announcement was made on the campaign trail. The DCLG [department for communities and local government] announcement was given to the press on Friday embargoed until Monday morning. The visit took place on Saturday. No announcement was made on Saturday and no announcement was publicised on Saturday. Following the visit the regional Liberal Democrat group, with the approval of the DCLG, put out a press release to follow the government announcement on Monday."

A cabinet office spokesman said: "We have not received a letter. But we will respond in due course."

The Lib Dems will be acutely embarrassed if they have broken election rules. The Oldham East and Saddleworth byelection is being held after Watkins, the Lib Dem candidate at the general election, won a court case. This barred the winning Labour candidate, Phil Woolas, from sitting at Westminster after two high court judges ruled that he had broken electoral law.

The judges ruled that Woolas had lied about Watkins after claiming the Lib Dem had "wooed" Islamic extremists. Watkins brought the case the case under Section 106 of the Representation of the People Act (1983) which makes it an offence for anyone to publish "any false statement of fact in relation to the candidate's personal character or conduct" to prevent them being elected.

Yvette Cooper, the shadow foreign secretary, criticised the Stunell announcement when she visited the constituency earlier in the day. The former housing minister said: "This is a sure sign of desperation from the Liberal Democrats who clearly don't want to campaign on things like VAT and tuition fees that the government had already announced before the campaign started. Nick Clegg needs to tell us swiftly whether this announcement was agreed with the prime minister and the cabinet secretary, Sir Gus O'Donnell, or not."

The row last night came as the Lib Dems and Labour, who were 103 votes apart in the seat in the general election, made a final push ahead of Thursday's poll which is the first electoral test since the coalition was formed last May. Polls over the weekend suggested that Labour, which has held the seat since 1997, is on course for a comfortable victory over the Lib Dems.

An ICM poll for the Mail on Sunday and a Populus poll for the Sunday Telegraph gave Labour a 17 point lead over the Lib Dems and indicated that the Tory vote has weakened. The polls suggest that some Tories may be "lending" their votes to their coalition partners, though a greater number of former Lib Dem voters appear to be turning to Labour, possibly in protest at the government's spending cuts.

A loss on Thursday would be a blow to Clegg and would confirm that the Lib Dems will face a bumpy ride as they are blamed for helping to impose £81bn of spending cuts.

Lib Dem nervousness over their role in implementing the most drastic cuts in a generation may explain why the party used the weekend visit by its housing minister to highlight a £100m scheme to boost the provision of affordable housing.

Stunell, who was one of the four Lib Dems who negotiated the coalition agreement with the Tories last May, described empty houses as a "scandal" and pledged to spend £100m to bring thousands back into use, including 2,338 in Oldham. In his press release he said: "We're giving local councils, including Oldham, powerful new incentives to bring them back into use."