About 250 MPs employ relatives
Spouses who are employed by MPs are preparing to look into legal action if they are barred from their jobs.
An inquiry into MPs' expenses is due to report back on 4 November but reports suggest it will recommend a ban on family members on the Commons payroll.
The Unite union has told the BBC that it will hold a meeting the same day for concerned staff.
If the inquiry favours a complete ban on MPs employing relatives, Unite says there are grounds for unfair dismissal.
Even if it recommends a ban is phased in over the lifetime of the next Parliament, Unite says a legal challenge may still be possible.
And it argues that as more wives are employed than husbands - there may be grounds for a sexual discrimination case.
BBC political correspondent Iain Watson said it could mean MPs' staff are at loggerheads with the House of Commons authorities.
Suzy Gale, who has worked for her husband the Conservative MP Roger Gale for more than 26 years, is among those who are concerned about the inquiry's findings.
She has written to conciliation service Acas asking for clarification of her employment position.
It is not yet known what recommendations the independent committee on standards in public life will make, when it publishes its report next week.
But party leaders have indicated they will adopt the recommendations - barring exceptional circumstances - in an effort to restore trust in the system following the MPs' expenses scandal.
During the inquiry's hearings, it was revealed that about 250 MPs employ relatives.
Chairman Sir Christopher Kelly said the situation "looks odd" while the committee noted that other legislatures had moved to ban the practice.
Many people who wrote to the inquiry said it should be banned altogether but several MPs, even those who do not employ relatives, defended their colleagues' right to do so.
While claims under the second homes allowance were at the heart of the scandal, there has also been much focus on MPs who employ relatives.
Last year MP Derek Conway had the Tory whip withdrawn after being criticised for paying his sons too much public money.