The Glazer family has moved to block any future hostile takeover of Manchester United by quietly altering the club's constitution, in a move that will further enrage the club's fans.

The changes – almost certainly designed to protect the Glazers' control of the club if the family cashes in further shares – is revealed in regulatory documents published as part of the club's planned flotation in New York. The float stands to net the Glazers around $150m (£96m), despite previous assurances that proceeds would go towards paying down the club's debt.

The US filing warns potential investors: "Anti-takeover provisions in our organizational documents and Cayman Islands law [where Manchester United are incorporated] may discourage or prevent a change of control, even if an acquisition would be beneficial to our shareholders, which could depress the price of our shares and prevent attempts by our shareholders to replace or remove our current management."

The filing goes on to say that the club's "amended and restated memorandum and articles of association" now permit the Glazers to issue new shares "from time to time, with such rights and preferences as they consider appropriate. Our board of directors could also authorize the issuance of preference shares with terms and conditions and under circumstances that could have an effect of discouraging a takeover or other transaction".

The Glazers are only selling around 10% of the club through the stock market listing, so they would be able to block any takeover bid launched immediately after the float. However, financial experts said that the new anti-takeover clauses would protect their position if they needed to raise cash in the future by selling down their holding.

The flotation documents also show that the Glazers have retained the option to sell an additional 2.5m of their shares, which would bolster their proceeds from the offering by $45m.

Michael Moritz, a Cardiff-born Silicon Valley investor who is also a Manchester United fan and critic of the Glazers, said: "The anti-takeover provisions further protect the Glazers. It is the financial equivalent of armed robbers leaving the scene of a crime and throwing nails on the road to stop pursuers.A pound of potatoes will be a better investment than the purchase of shares in Manchester United's stock offering. The only people who will be better off with this offering are the Glazers".

Neither Manchester United nor Jefferies, the club's main adviser on the listing, returned phone calls or emails.

Monday evening's statement – which described United as an "emerging growth company" despite revenues slumping by up to 5% in the last financial year – shows that the club will be valued at around $3bn if the listing goes off successfully. Assuming United can find enough buyers, the shares will begin trading next month.

However, it is still far from clear that the club will be able to sell enough shares at what the Glazers consider an acceptable price, and concerns over the valuation have previously forced the club to abandon plans to list its shares in Hong Kong and then in Singapore. The investment bank Morgan Stanley is also believed to have stepped away from the flotation because of fears that the Glazer family had pinned too high a valuation on the club.

Much of the investor concern comes down to the club's massive debt, which stood at £437m at the end of June, and how the balance sheet is potentially weighing the club down.

Andy Green, a football finance writer behind the andersred blog, calculates that £520m has been taken out of United since the Glazers took the club over in 2005, with most of that figure being accounted for via interest and fees related to the club's borrowings. Meanwhile, of the £520m, £38m has been paid directly to the Glazers via £28m in consultancy fees to their companies and a £10m dividend.

Apart from raising money for the Glazers, a successful float of Manchester United will achieve two further aims. Firstly, it will raise around $150m to pay down debts. Second it will give the club a financial valuation, which the Glazers will eventually need if they are to cash in their investment by selling the club at some future point.

How much United are worth is crucial to the balance of the family's finances. Wealth-X, a consultancy that specialises in high net worth individuals, estimates Malcolm Glazer's fortune at $2.7bn, $1.3bn of which is tied to United. His stake in the Tampa Bay Buccaneers is worth another $980m and First Allied, his ailing shopping malls business, another $8.5m. The rest is cash shares and property.