USA open major championship not a RG. There are tier RG`s in which you can play in against fellow players from the same tier.
Best of the best play in that tournament
Fair is fair post a score under the cut line what ever tier you play of.
According to the website I looked at.
The U.S. Open is open to any professional, or to any amateur with an up-to-date USGA Handicap Index not exceeding 1.4. Players (male or female) may obtain a place by being fully exempt or by competing successfully in qualifying. The field is 156 players.
About half of the field is made up of players who are fully exempt from qualifying. There are 17 full exemption categories, including winners of the U.S. Open for the last ten years and the other three majors for the last five years, the top 30 from the previous year's PGA Tour money list, the top 15 from the previous year's European Tour money list, and the top 50 in the Official World Golf Rankings as of two weeks before the tournament. Starting in 2011, the top 50 in the Official World Golf Rankings as of the tournament date will also be exempt; this will allow players who enter the top 50 after the initial cutoff (such as Justin Rose and Rickie Fowler in 2010) to gain entry.[1] For 2012 and beyond, the USGA will eliminate the exemptions for top money winners on the PGA and European Tours, instead inviting the top 60 in the Official World Golf Rankings at the relevant dates.[1]
Potential competitors who are not fully exempt must enter the Qualifying process, which has two stages. Firstly there is Local Qualifying, which is played over 18 holes at over 100 courses around the United States. Many leading players are exempt from this first stage, and they join the successful local qualifiers at the Sectional Qualifying stage, which is played over 36 holes in one day at several sites in the U.S. and one each in Europe and Japan. There is no lower age limit and the youngest-ever qualifier was 15-year-old Tadd Fujikawa of Hawaii, who qualified in 2006.
The purse at the 2010 U.S. Open was $7.5 million, and the winner's share was $1.35 million. The PGA European Tour uses conversion rates at the time of the tournament to calculate the official prize money used in their Race to Dubai (€6,244,276 in 2010). In line with the other majors, winning the U.S. Open gives a golfer several privileges that make his career much more secure if he is not already one of the elite players of the sport. U.S. Open champions are automatically invited to play in the other three majors (the Masters, the Open Championship (British Open), and the PGA Championship) for the next five years, as well as the Players Championship, and they are exempt from qualifying for the U.S. Open itself for 10 years. They may also receive a five-year exemption on the PGA Tour, which is automatic for regular members. Non-PGA Tour members who win the U.S. Open have the choice of joining the PGA Tour either within 60 days of winning, or prior to the beginning of any one of the next five tour seasons. Finally, U.S. Open winners receive automatic invitations to three of the five senior majors once they turn 50; they receive a five-year invitation to the U.S. Senior Open and a lifetime invitation to the Senior PGA Championship and Senior British Open.
The top 15 finishers at the U.S. Open are fully exempt from qualifying for the following year's Open, and the top eight are automatically invited to the following season's Masters.