Liberal Democrat MP Lembit Opik intervened over threats to deport his pop star girlfriend Gabriela Irimia to Romania, the party has confirmed.
The Home Office denied Miss Irimia and her sister Monica - the Cheeky Girls - further leave to remain in the summer.
Mr Opik passed documentation on to the singers' constituency MP and spoke to a Home Office minister about the matter.
But he had shown "total propriety" and had not lobbied on their behalf, a Liberal Democrat spokesman said.
The Lib Dems say Mr Opik passed on documents about the case to Michael Foster, MP for Hastings, East Sussex, which contains the sisters' Rye home, to inform him of the situation.
Mr Opik also mentioned the matter to Immigration minister Liam Byrne when they met in a corridor, reiterating that he knew the women in a personal capacity, the spokesman added.
A Lib Dem spokesman said: "Lembit acted with total propriety with regard to this matter.
"He did what any MP would do, and referred the matter to the appropriate Member of Parliament.
"At no stage did he lobby anybody on this matter. He simply referred the issue through the relevant and proper channels."
Mr Opik announced at the weekend that he was splitting up with his longterm partner, the television weather presenter Sian Lloyd.
The MP, who is the Lib Dem spokesman on Wales and Northern Ireland, said the couple had separated "some time ago" and it was "no secret" that he was seeing Miss Irimia.
He assured party officials there was no overlap in the relationships.
The Cheeky Girls arrived in the UK from their native Romania in 2002 and shot to fame with appearances on reality TV shows Popstars: The Rivals and Model Behaviour.
Their first single The Cheeky Song (Touch My Bum) reached number two in the charts in 2004.
The duo faced bankruptcy this summer when Telstar, their record company, collapsed.
Romania is due to join the European Union in January, which means its citizens will have the right to travel freely within Europe.
Self-employed people from the two countries are free to work in the UK after 1 January. The Evening Standard reports that a Whitehall source said that the Cheeky Girls were not likely to be pursued for deportation.
Immigration minister Liam Byrne, asked about the case by the BBC, said he could not comment on individual cases.
On Tuesday Miss Irimia told GMTV: "Our relationship is really genuine and it's not out of a pantomime or anything like that.
"We understand each other really well and we are looking for a long relationship here."