The Lord Advocate has lodged an appeal against the sentence imposed on the man convicted of the Lockerbie bombing.
Megrahi was jailed for life for the bombing
Abdelbaset ali Mohmed al-Megrahi was told last month that he would have to serve 27 years before he could apply for parole.
Colin Boyd has now lodged an appeal, arguing that the punishment part of the sentence is unduly lenient.
He is also challenging the court's view that 30 years is the maximum punishment part which can be imposed.
Megrahi was found guilty of the 1988 bombing after an 84-day trial under Scottish law in the Netherlands.
He was convicted of murdering the 270 people who died when Pan Am Flight 103 exploded over the Scottish town of Lockerbie.
Apply for parole
Megrahi was sentenced to life in prison, with a recommendation that he serve at least 20 years.
Human rights laws have since been introduced in Scotland which mean that lifers must be told exactly how long they must serve before they can apply for parole.
Megrahi was brought before the High Court in Glasgow last month for the punishment part of his sentence to be set.
Lord Sutherland told the 51-year-old that he would have to serve 27 years before he could apply for parole.
That sentence was backdated to 1999, when he was first taken into custody.
Tam Dalyell, the Labour MP for Linlithgow, said he was unhappy about the Lord Advocate's appeal.
"It looks as though pressure from the American relatives of the victims has caused the Lord Advocate to do this," Mr Dalyell said.
"I fervently believe that Mr Megrahi is innocent."
In September, the Scottish Criminal Cases Review Commission was asked to investigate the case.
The independent body is charged with investigating possible miscarriages of justice.
Solicitors acting on behalf of Megrahi have requested that it review his conviction.
His lawyer Eddie MacKechnie said the decision to appeal the punishment part of the sentence was "irrelevant".
"The issue is one of whether this is the man guilty of the Lockerbie murders," he said.
"I am convinced he is utterly innocent of the murders and I hope that very soon the commission will begin their work in earnest to discover whether this is a case fit to be sent back to the appeal court."
However, Mr Boyd's move was welcomed by George Williams, one of the relatives of the American victims.
He said: "They got the trigger guy but they never got (Libyan leader Muammar) Gaddafi and there's no chance of that happening now.
"I am satisfied that they got the right guy and any increase in his sentence would be fine by me."