Britney Spears’ pregnant little sister Jamie Lynn’s relationship with fiancé Casey Aldridge is under strain over his refusal to sign a pre-nuptial agreement.

The 17-year-old actress, star of Nickelodeon’s kids show Zoey 101, accepted Casey’s proposal at the end of March – four months after the teen confirmed her shock pregnancy on the cover of a U.S. weekly magazine.

Jamie Lynn has reportedly asked Casey to sign a pre-nuptial agreement upon the insistence of her mother Lynne.

Testing times?: Pregnant Jamie Lynn Spears with fiance Casey Aldridge in McComb, Mississippi, earlier this month

Lynne, 53, previously convinced her eldest daughter Britney to sign a pre-nup when she wed aspiring rapper Kevin Federline in September 2004 after a whirlwind six month courtship.

Lynne had the contract drawn up last month to protect Jamie Lynn’s estimated few million dollar fortune, but Casey does not want to sign it.

A friend tells In Touch magazine: “Casey doesn’t want to sign the prenuptial agreement.

“It’s really causing a strain for everyone. It’s been going for a month and he still hasn’t signed it.

“Even though Jamie Lynn is excited to get married, because of everything, the couple hasn’t set a wedding date.”

Jamie Lynn is expected to give birth next month in her native Kentwood, Louisiana, where she wants to bring the child up.

High school student Jamie Lynn has been dating the 19-year-old piper for over two years after meeting at church.

Announcing her pregnancy in December, Jamie Lynn said: “It was a shock for both of us, so unexpected. I was in complete and total shock and so was he.

“As soon as I found out for sure from the doctor, I took two weeks to myself where I didn't tell anybody.

“Only one of my friends knew because I needed to work out what I would do for myself before I let anyone's opinion affect my decision. Then I told my parents and my friends. I was scared, but I had to do what was right for me.”

Sisterly devotion: Britney Spears and Jamie Lynn, pictured late last year, are very close