An SNP MSP has accused the Electoral Commission of a whitewash after it decided not to report Wendy Alexander to prosecutors.
Wendy Alexander should pay for her mistake, says Alex Neil MSP
Alex Neil MSP claimed the commission had shown itself to be incompetent by failing to refer Ms Alexander for accepting an "impermissible donation".
The commission insists its 10-week investigation was thorough and its conclusions independent.
The MSP and Labour peer Lord Foulkes accused Mr Neil of being a bad loser.
Following the verdict, Ms Alexander expressed "deep regret" that her campaign team had ever accepted the £950 donation from Jersey-based businessman Paul Green.
The commission ruled she had taken "significant" steps to comply with the law, though not all that was required, and therefore had decided not to report her to prosecutors.
The Crown Office confirmed it saw no basis for further inquiry into the case following the Electoral Commission ruling.
However, Mr Neil said of the verdict: "It's incredible. It's a total whitewash.
"How could this be regarded as a sane or a sensible decision when Wendy herself admitted she had broken the law? If you break the law you have to take the consequences.
"I think coming on top of the Scottish election fiasco last year, the credibility of the Electoral Commission is in total tatters."
The commission had proven it was neither a competent nor an independent organisation, he claimed.
Mr Neil added: "We are in the absolutely crazy situation where the law has been broken and nothing has been done about it and quite frankly if you are going to have rules, when you break the rules you have to be properly dealt with."
However, on Thursday, the commission said it was "not in the public interest" to report Ms Alexander to the Crown Office or Procurator Fiscal Service on the issue of whether accepting the donation was an offence.
It also ruled there was no evidence to establish her campaign team had sought to conceal or give false information surrounding the cash.
Lord Foulkes accused Mr Neil of pursuing a vendetta against Ms Alexander.
Speaking on BBC Radio's Good Morning Scotland programme, he said: "Wendy Alexander has suffered a vendetta from the SNP, and by Alex Neil and Roseanna Cunningham in particular - personal abuse and 10 weeks of pressure.
"She had dealt with this with great inner strength and I think she has come out of it strengthened by what has happened."
The commission has rejected Mr Neil's criticisms.
"Commissioners are not appointed by government and there are strict rules about previous political activity by commissioners," it said in a statement.
"Commissioners cannot be a member of a political party, and cannot, by law, have been an office holder or employee of a political party, or held elective office, for a period of 10 years prior to their appointment," it added.
The Crown Office said its officials were consulted so the commission could reach a decision "on the basis of all relevant evidence".
A Crown Office spokesman said: "It is a matter for the commission to investigate alleged breaches of the Political Parties, Elections and Referendums Act 2000 and thereafter determine whether the allegation should be referred to the Crown Office and Procurator Fiscal Service."
He went on: "COPFS has been fully briefed on the commission's inquiries and, standing its decision not to refer the case to COPFS, we do not consider that there is any proper basis for further inquiry into these matters."
Meanwhile, Lord Foulkes complained to First Minister Alex Salmond over Mr Neil's criticism.
"Mr Neil's comments are an absolute disgrace," he said.
"To call the decision a whitewash and launch a vindictive, personal attack on a member of an independent regulator, which all parties voted for, is outrageous and even beneath the usual gutter politics we expect from Alex Neil."