The Parliamentary Commissioner for Standards has confirmed it has received a formal complaint over Barry McElduff's Kingsmill video tweet.
The West Tyrone MP was suspended by his party, with full pay, after he tweeted a video of himself with a loaf of bread on his head on the anniversary of the Kingsmill massacre.
Mr McElduff apologised and said his intention was not to cause hurt. He insisted the video was not in reference to the sectarian killings of 10 workmen in the south Armagh village and he had not realised the significance of the date.
Sinn Fein described his actions as inexcusable and indefensible.
MPs tabled an early day motion on the tweet stating it would be "wise if he resigned his seat".
The Westminster Standards Commissioner confirmed a formal complaint had been made. However, it will not open an investigation into the matter as there is an ongoing police probe. Police and any subsequent court proceedings will take precedence over its opening of any investigation.
The office said that while he is an abstentionist MP he is still subject to the code of conduct for MPs.