SUPER League clubs have been warned they could face additional sanctions, including the deduction of points, if they call off matches in an attempt to gain an unfair advantage.

The postponement of Sunday's fixtures at Hull and Hull KR takes the number of matches lost so far during the latest upsurge in coronavirus infections to 12.

All 12 clubs have had at least one fixture called off and attempts are being made to rearrange the bulk of them but two games were cancelled after Castleford and Huddersfield said they were unable to raise teams.

Both the Giants and the Tigers failed to reach the threshold of seven for players impacted by Covid-19 and the games were awarded to their opponents with 24-0 scorelines.

Karen Moorhouse, the Rugby Football League's chief regulatory officer, told a media briefing on Sunday that clubs who failed to fulfil a fixture are also being referred to the governing body's compliance department.

"Clearly not fulfilling a match is a breach of the operational rules," she said. "If there was any suggestion that they had done that to gain any sort of advantage there could be significant additional sanctions imposed.

"The range of sanctions by an operational rules tribunal range from a fine but could also include a deduction of points as an extreme example.

"This idea that a club would deliberately pick and choose which matches to play is just not the case. There would be significant compliance sanctions if anyone tried to go down that route."

Salford were fined £15,000, half of it suspended, for failing to fulfil a fixture against Warrington last October.

Envisaging further disruption, the RFL decided before the season began that league positions would again be determined by win percentage and, as it stands, clubs must play a minimum 18 matches matches to qualify for the top-six play-offs but Moorhouse says that could change.

"The situation we find ourselves in is perhaps not one that any of us envisaged we would be in at the start of the season," she said.

"There is ongoing dialogue with Super League and the clubs around whether that framework remains right."

Moorhouse says the recent increase in positive tests among Super League clubs is in line with the national trend and statistics show the rugby league heartland has been particularly badly affected.

"The 20-39 age group is particularly impacted currently which is precisely the range that covers our players," she said.

"Communities where Covid rates are the highest across the UK include a significant number in our heartlands - Wigan, Rochdale and Oldham all jump out.

"If you looked at this a couple of weeks ago, it almost read like a rugby league league table."

Moorhouse, who says the RFL is bracing itself for a further increase in infections with the end of lockdown restrictions, scheduled for July 19, also offered an explanation as to why top-flight players have been affected much worse than those in the largely part-time Championship and League 1.

"One of the factors is that they do train together more," she said. "They have more frequent training sessions and, therefore, if you do have an issue you may have had a couple of training sessions before it's spotted and therefore there is a risk it may have already spread.

"Championship players possibly spend less time with each other outside of the club than Super League players which may contribute to transmission and people being identified as close contacts."

Moorhouse says the RFL is not forcing clubs to impose vaccinations on their players but have offered encouragement.

"We believe that very strongly as a governing body about the benefits of vaccinations from a player health perspective and also from a broader sport perspective but ultimately we're not - at the moment - mandating that players have to be vaccinated," she said.

"I'd encourage any player who has any questions on vaccinations to go and speak to their medical staff."

Moorhouse, who says there are no discussions about scrapping relegation for the second year in a row, also revealed contingency plans were drawn up in the event that Covid impacts next Saturday's Challenge Cup final between Castleford and St Helens at Wembley.

Warrington and Hull, the two beaten semi-finalists, have been stood down, although their ability to step in as emergency finalists would have been in grave doubt due to a Covid outbreak at both clubs.

Moorhouse said: "We have worked closely with the clubs to make sure that they are absolutely doubling down on protocols to minimise and mitigate the risk of any of the players getting Covid.

"We have also done some contingency planning that did include that, had there been a shutdown early on that meant a club wasn't going to be able to make the final, we would have brought in one of the losing semi-finalists to play that match.

"We are now just about past that point at which it would have been a possibility. But we still do have contingency plans in place."