Amazon increased the minimum purchase regular customers must make in order to qualify for free shipping. The online retailer hiked it to $49 in hopes that more buyers will opt to become Prime members.

For the longest time, those who are not Prime service subscribers enjoyed free shipping for a minimum purchase of $25, before the company raised it to $35 in 2013.

There is good news for book lovers, though.According to Amazon, the minimum purchase of books to qualify for free shipping remains at $25. Also included in this category are audiobooks on CDs. For other items, the new rate will be applied.

Under free shipping, the purchased items will be delivered within five to eight business days after all the items have become available to be sent out. The time frame varies for preordered items.

Last year, Amazon paid $5 billion in net shipping costs, which is a 19 percent increase compared to the previous year. The figure is equivalent to approximately 5.1 percent of total sales, with the costs for shipping becoming even steeper.

Savings on shipping costs by raising the minimum purchase amount for free shipping is likely only a bonus to the company, however. Amazon is hoping that the increase of the minimum amount for free shipping will attract more customers to subscribe to a Prime membership, which costs $99 per year.

Prime members are able to receive purchased items within two days, while items eligible for the Prime Now service, within only 1 hour. Shipping for Prime members is free.

In addition to free and fast shipping, Prime members have access to several other Amazon perks such as exclusive Amazon Prime Video offers, Amazon Prime Music unlimited streaming, unlimited Amazon Prime Photos storage, and restaurant delivery in select areas in the United States.

A report, released earlier this year, said that almost half of the households in the country have Amazon Prime memberships, while another report revealed that non-Prime buyers suffer longer waiting time before they get purchased items.