Harriet Harman won last year's Labour deputy leadership race
The Electoral Commission has written to Labour's Harriet Harman to remind her that failing to report donations on time "is a serious matter".
Donations of £6,001 and loans totalling £58,000 last year for her deputy Labour leadership bid were declared late.
But the commission said that "having reviewed all the evidence" they would not refer the late reporting to police.
Meanwhile police have dropped their inquiry into Ms Harman's acceptance of a proxy donation of £5,000.
Ms Harman's late declarations consisted of £5,000 from the Muslim Friends of Labour and £1,001 from Baroness Ashton, made in July which were not reported until September.
All "regulated donees" are expected to report any donation over £1,000 to the Electoral Commission, within 30 days of accepting it.
Ms Harman was also late in reporting two loans totalling £58,000 and the return of an "impermissible" loan of £1,500 from Alun Hayes.
A spokesman for the Electoral Commission said: "Having reviewed all the evidence, the Commission has decided not to refer this late reporting to the police.
"However, we have written to Harriet Harman making clear that failure to report on time is a serious matter and that we expect her to comply with the rules.
"Compliance with the rules on reporting donations and loans is essential to ensure integrity, transparency and confidence in the political process."
Harriet Harman, Peter Hain and Alan Johnson all faced questions over donations to their deputy leadership campaigns, in the wake of wider revelations about Labour Party funding.
It emerged in November that a property developer, David Abrahams, had donated more than £660,000 to the party over several years, under other people's names - in breach of electoral law. Labour's general secretary Peter Watt resigned over it.
It also emerged Ms Harman had accepted a £5,000 donation from one of his proxy donors - Janet Kidd - although she said she had not known of the link and accepted it in "good faith" from Ms Kidd.
Police have decided to take no further action against Ms Harman over the proxy donation, but are continuing to investigate the wider issue of proxy donations to the party.
A Metropolitan Police spokesman said: "One such matter related to a single donation received by the deputy leadership campaign of an individual.
"The Metropolitan Police Service has investigated this matter and after consultation with the Crown Prosecution Service decided that no further action will be taken in relation to the allegation against that individual.
"The wider investigation continues and the MPS will not be making further comment on the investigation at this stage."
Peter Hain stepped down as work and pensions secretary in January to "clear his name" after his case was referred to police.
He discovered some donations had not been properly registered, and after a full investigation said more than £103,000 had not been reported.