The Swiss club Sion have announced that they have filed a criminal complaint against members of Fifa's executive committee over its threat to suspend Switzerland from world football.

Sion said on their website that the threat made on 17 December by football's ruling body amounts to unacceptable blackmail and a breach of basic legal rules.

Fifa said it wanted the Swiss national association to discipline Sion within one month over a long-running legal battle.

Sion are contesting their expulsion from the Europa League in September for fielding players signed during a Fifa transfer ban imposed in 2009.

If the suspension takes effect, Basel would be prevented from playing Bayern Munich in the Champions League round of 16. The first leg is scheduled for 22 February.

Basel knocked Manchester United out of the Champions League at the group stage, leading to suggestions that the English champions may be reinstated in the competition, though Uefa, the European governing body, has refused to comment.