My take is that it's a sign that the company is running low on cash and it is a sign that it has recognized the need to reduce its burn rate and it is a sign that the company is looking to reduce its expenses in regard to programming and it is a sign that your last invoice might not be paid and a sign that your invoices prior to the last invoice might not be paid. If you let them stack up.

Whether or not it's acceptable depends on which other options are available. If those options make the pay reduction acceptable, my advice is to require pre-payment in exchange for the reduction in rate.

The company has acknowledged pending cash flow problems. If the company balks at prepayment, it means that not paying you for work you have done is an option the company is considering as part of its survival plan.

There's no reason to trust the company to pay more than they trust you to do the work.

Good luck.