First Minister Mark Drakeford imposed restrictions on sporting events in Wales, effectively meaning professional games are behind closed doors.
There is no date set for when measures could be eased, with the next review scheduled for 7 January.
Wales are due to host Scotland in Cardiff on 12 February.
Wayne Pivac's side are also scheduled to meet France on 11 March and Italy eight days later at the Principality Stadium, meaning Wales could face the prospect of playing over half the competition on home soil with no fans.
As things stand, sporting events in England have no restrictions, so Wales' visit to Twickenham on 26 February will be played before a full house of 82,000, provided spectators can prove full vaccination status or a negative lateral flow test.
Wales launch the defence of their Six Nations title against Ireland in Dublin on 5 February, with current restrictions of 5,000 fans there.
Scotland also has restrictions on spectator numbers of 500, France has a limit of 5,000 fans and Italy has a Covid pass system in place after tightening restrictions in December.
The WRU lost £13.5m in matchday revenue during the 2021 Six Nations after home games against England and Ireland were played behind closed doors.
The WRU's preference is to play home fixtures this year in front of full crowds in Cardiff and hope restrictions will be lifted in time.
There are major logistical issues in relocating matches including tickets already sold for the games, availability of stadiums and public health concerns, with the prospect of thousands of Welsh fans travelling to England and back.
The WRU has also stressed throughout the pandemic they will abide by and support Welsh government's policy on public health. The governing body will also rely on future financial assistance from the Welsh government.
This is the second time the WRU has considered moving games to England after exploring the possibility for the Autumn Nations Cup in November 2020 when the Principality Stadium was used as a field hospital.
On that occasion Wales ended up playing their matches at Parc y Scarlets in Llanelli, with no spectators.
Wembley Stadium will not be able to host any Welsh Six Nations games this year because they are preparing for England international football games in March.
Other venues with the capacity required would be West Ham's London Stadium, Arsenal's Emirates Stadium or the Tottenham Hotspur Stadium, which WRU officials visited in late 2020.
That venue would prove troublesome this time around because two of the three weekends clash with Tottenham home matches in the Premier League.
Six Nations organisers are monitoring the situation with meetings this week which they hope will offer more clarity on the situation in each of the countries.